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/*
* Python JIT - DWARF .eh_frame builder
*
* This file contains the DWARF CFI generator used to build .eh_frame
* data for JIT code (perf jitdump and other unwinders).
*/
#include
"Python.h"
#include
"pycore_jit_unwind.h"
#include
"pycore_lock.h"
#if
defined(
PY_HAVE_JIT_GDB_UNWIND
)
# include
"jit_unwind_info.h"
# if
!
JIT_UNWIND_INFO_SUPPORTED
# error
"JIT unwind info was not generated for this target"
# endif
#endif
#if
defined(
PY_HAVE_PERF_TRAMPOLINE
) \
||
defined(
PY_HAVE_JIT_GDB_UNWIND
) \
||
defined(
PY_HAVE_JIT_GNU_BACKTRACE_UNWIND
)
#if
defined(
PY_HAVE_JIT_GDB_UNWIND
)
# include
<elf.h>
#endif
#if
defined(
PY_HAVE_JIT_GNU_BACKTRACE_UNWIND
)
/*
* libgcc exposes frame registration entry points, but GCC's public headers
* on some distributions do not declare them even though the symbols are
* available in libgcc_s.
*/
void
__register_frame
(
const
void
*
);
void
__deregister_frame
(
const
void
*
);
#endif
#include
<stdio.h>
#include
<string.h>
// =============================================================================
// DWARF CONSTANTS
// =============================================================================
/*
* DWARF (Debug With Arbitrary Record Formats) constants
*
* DWARF is a debugging data format used to provide stack unwinding information.
* These constants define the various encoding types and opcodes used in
* DWARF Call Frame Information (CFI) records.
*/
/* DWARF Call Frame Information version */
#define
DWRF_CIE_VERSION
1
/* DWARF CFA (Call Frame Address) opcodes */
enum
{
DWRF_CFA_nop
=
0x0
,
// No operation
DWRF_CFA_offset_extended
=
0x5
,
// Extended offset instruction
DWRF_CFA_def_cfa
=
0xc
,
// Define CFA rule
DWRF_CFA_def_cfa_register
=
0xd
,
// Define CFA register
DWRF_CFA_def_cfa_offset
=
0xe
,
// Define CFA offset
DWRF_CFA_offset_extended_sf
=
0x11
,
// Extended signed offset
DWRF_CFA_advance_loc
=
0x40
,
// Advance location counter
DWRF_CFA_offset
=
0x80
,
// Simple offset instruction
#if
defined(
__aarch64__
)
DWRF_CFA_AARCH64_negate_ra_state
=
0x2d
,
// Toggle return address signing state
#endif
DWRF_CFA_restore
=
0xc0
// Restore register
};
/*
* Architecture-specific DWARF register numbers
*
* These constants define the register numbering scheme used by DWARF
* for each supported architecture. The numbers must match the ABI
* specification for proper stack unwinding.
*/
enum
{
#ifdef
__x86_64__
/* x86_64 register numbering (note: order is defined by x86_64 ABI) */
DWRF_REG_AX
,
// RAX
DWRF_REG_DX
,
// RDX
DWRF_REG_CX
,
// RCX
DWRF_REG_BX
,
// RBX
DWRF_REG_SI
,
// RSI
DWRF_REG_DI
,
// RDI
DWRF_REG_BP
,
// RBP
DWRF_REG_SP
,
// RSP
DWRF_REG_8
,
// R8
DWRF_REG_9
,
// R9
DWRF_REG_10
,
// R10
DWRF_REG_11
,
// R11
DWRF_REG_12
,
// R12
DWRF_REG_13
,
// R13
DWRF_REG_14
,
// R14
DWRF_REG_15
,
// R15
DWRF_REG_RA
,
// Return address (RIP)
#elif
defined(
__aarch64__
)
&&
defined(
__AARCH64EL__
)
&&
!defined(
__ILP32__
)
/* AArch64 register numbering */
DWRF_REG_FP
=
29
,
// Frame Pointer
DWRF_REG_RA
=
30
,
// Link register (return address)
DWRF_REG_SP
=
31
,
// Stack pointer
#else
# error
"Unsupported target architecture"
#endif
};
// =============================================================================
// ELF OBJECT CONTEXT
// =============================================================================
/*
* Context for building ELF/DWARF structures
*
* This structure maintains state while constructing DWARF unwind information.
* It acts as a simple buffer manager with pointers to track current position
* and important landmarks within the buffer.
*/
typedef
struct
ELFObjectContext
{
uint8_t
*
p
;
// Current write position in buffer
uint8_t
*
startp
;
// Start of buffer (for offset calculations)
uint8_t
*
fde_p
;
// Start of FDE data (for PC-relative calculations)
uintptr_t
code_addr
;
// Address of the code section
size_t
code_size
;
// Size of the code section
}
ELFObjectContext
;
// =============================================================================
// DWARF GENERATION UTILITIES
// =============================================================================
/*
* Append a null-terminated string to the ELF context buffer.
*
* Args:
* ctx: ELF object context
* str: String to append (must be null-terminated)
*
* Returns: Offset from start of buffer where string was written
*/
static
uint32_t
elfctx_append_string
(
ELFObjectContext
*
ctx
,
const
char
*
str
) {
uint8_t
*
p
=
ctx
->
p
;
uint32_t
ofs
=
(
uint32_t
)(
p
-
ctx
->
startp
);
/* Copy string including null terminator */
do
{
*
p
++
=
(
uint8_t
)
*
str
;
}
while
(
*
str
++
);
ctx
->
p
=
p
;
return
ofs
;
}
/*
* Append a SLEB128 (Signed Little Endian Base 128) value
*
* SLEB128 is a variable-length encoding used extensively in DWARF.
* It efficiently encodes small numbers in fewer bytes.
*
* Args:
* ctx: ELF object context
* v: Signed value to encode
*/
static
void
elfctx_append_sleb128
(
ELFObjectContext
*
ctx
,
int32_t
v
) {
uint8_t
*
p
=
ctx
->
p
;
/* Encode 7 bits at a time, with continuation bit in MSB */
for
(; (
uint32_t
)(
v
+
0x40
) >=
0x80
;
v
>>=
7
) {
*
p
++
=
(
uint8_t
)((
v
&
0x7f
) |
0x80
);
// Set continuation bit
}
*
p
++
=
(
uint8_t
)(
v
&
0x7f
);
// Final byte without continuation bit
ctx
->
p
=
p
;
}
/*
* Append a ULEB128 (Unsigned Little Endian Base 128) value
*
* Similar to SLEB128 but for unsigned values.
*
* Args:
* ctx: ELF object context
* v: Unsigned value to encode
*/
static
void
elfctx_append_uleb128
(
ELFObjectContext
*
ctx
,
uint32_t
v
) {
uint8_t
*
p
=
ctx
->
p
;
/* Encode 7 bits at a time, with continuation bit in MSB */
for
(;
v
>=
0x80
;
v
>>=
7
) {
*
p
++
=
(
char
)((
v
&
0x7f
) |
0x80
);
// Set continuation bit
}
*
p
++
=
(
char
)
v
;
// Final byte without continuation bit
ctx
->
p
=
p
;
}
/*
* Macros for generating DWARF structures
*
* These macros provide a convenient way to write various data types
* to the DWARF buffer while automatically advancing the pointer.
*/
#define
DWRF_U8
(
x
) (*p++ = (x)) // Write unsigned 8-bit
#define
DWRF_I8
(
x
) (*(int8_t*)p = (x), p++) // Write signed 8-bit
#define
DWRF_U16
(
x
) (*(uint16_t*)p = (x), p += 2) // Write unsigned 16-bit
#define
DWRF_U32
(
x
) (*(uint32_t*)p = (x), p += 4) // Write unsigned 32-bit
#define
DWRF_ADDR
(
x
) (*(uintptr_t*)p = (x), p += sizeof(uintptr_t)) // Write address
#define
DWRF_UV
(
x
) (ctx->p = p, elfctx_append_uleb128(ctx, (x)), p = ctx->p) // Write ULEB128
#define
DWRF_SV
(
x
) (ctx->p = p, elfctx_append_sleb128(ctx, (x)), p = ctx->p) // Write SLEB128
#define
DWRF_STR
(
str
) (ctx->p = p, elfctx_append_string(ctx, (str)), p = ctx->p) // Write string
/* Align to specified boundary with NOP instructions */
#define
DWRF_ALIGNNOP
(
s
) \
while ((uintptr_t)p & ((s)-1)) { \
*p++ = DWRF_CFA_nop; \
}
/* Write a DWARF section with automatic size calculation */
#define
DWRF_SECTION
(
name
,
stmt
) \
{ \
uint32_t* szp_##name = (uint32_t*)p; \
p += 4; \
stmt; \
*szp_##name = (uint32_t)((p - (uint8_t*)szp_##name) - 4); \
}
// =============================================================================
// DWARF EH FRAME GENERATION
// =============================================================================
static
void
elf_init_ehframe_perf
(
ELFObjectContext
*
ctx
);
#if
defined(
PY_HAVE_JIT_GDB_UNWIND
)
static
void
elf_init_ehframe_gdb
(
ELFObjectContext
*
ctx
);
#endif
static
inline
void
elf_init_ehframe
(
ELFObjectContext
*
ctx
,
int
absolute_addr
) {
if
(
absolute_addr
) {
#if
defined(
PY_HAVE_JIT_GDB_UNWIND
)
elf_init_ehframe_gdb
(
ctx
);
#else
Py_UNREACHABLE
();
#endif
}
else
{
elf_init_ehframe_perf
(
ctx
);
}
}
size_t
_PyJitUnwind_EhFrameSize
(
int
absolute_addr
)
{
/* The .eh_frame we emit is small and bounded; keep a generous buffer. */
uint8_t
scratch
[
512
];
_Static_assert
(
sizeof
(
scratch
) >=
256
,
"scratch buffer may be too small for elf_init_ehframe"
);
ELFObjectContext
ctx
;
ctx
.
code_size
=
1
;
ctx
.
code_addr
=
0
;
ctx
.
startp
=
ctx
.
p
=
scratch
;
ctx
.
fde_p
=
NULL
;
/* Generate once into scratch to learn the required size. */
elf_init_ehframe
(
&
ctx
,
absolute_addr
);
ptrdiff_t
size
=
ctx
.
p
-
ctx
.
startp
;
assert
(
size
<= (
ptrdiff_t
)
sizeof
(
scratch
));
return
(
size_t
)
size
;
}
size_t
_PyJitUnwind_BuildEhFrame
(
uint8_t
*
buffer
,
size_t
buffer_size
,
const
void
*
code_addr
,
size_t
code_size
,
int
absolute_addr
)
{
if
(
buffer
==
NULL
||
code_addr
==
NULL
||
code_size
==
0
) {
return
0
;
}
/* Generate the frame twice: once to size-check, once to write. */
size_t
required
=
_PyJitUnwind_EhFrameSize
(
absolute_addr
);
if
(
required
==
0
||
required
>
buffer_size
) {
return
0
;
}
ELFObjectContext
ctx
;
ctx
.
code_size
=
code_size
;
ctx
.
code_addr
=
(
uintptr_t
)
code_addr
;
ctx
.
startp
=
ctx
.
p
=
buffer
;
ctx
.
fde_p
=
NULL
;
elf_init_ehframe
(
&
ctx
,
absolute_addr
);
size_t
written
=
(
size_t
)(
ctx
.
p
-
ctx
.
startp
);
/* The frame size is independent of code_addr/code_size (fixed-width fields). */
assert
(
written
==
required
);
return
written
;
}
/*
* Generate a minimal .eh_frame for a single JIT code region.
*
* The .eh_frame section contains Call Frame Information (CFI) that describes
* how to unwind the stack at any point in the code. This is essential for
* unwinding through JIT-generated code.
*
* The generated data contains:
* 1. A CIE (Common Information Entry) describing the calling convention.
* 2. An FDE (Frame Description Entry) describing how to unwind the JIT frame.
*
* Two flavors are emitted, dispatched on the absolute_addr flag:
*
* - absolute_addr == 0 (elf_init_ehframe_perf): PC-relative FDE address
* encoding for perf's synthesized DSO layout. The CIE describes the
* trampoline's entry state and the FDE walks through the prologue and
* epilogue with advance_loc instructions. This matches the pre-existing
* perf_jit_trampoline behavior byte-for-byte.
*
* - absolute_addr == 1 (elf_init_ehframe_gdb): absolute FDE address
* encoding for the GDB JIT in-memory ELF. The CIE describes the
* steady-state frame layout (CFA = %rbp+16 / x29+16, with saved fp and
* return-address column at fixed offsets) and the FDE emits no further
* CFI. The same rule applies at every PC in the registered region,
* which is correct for executor stencils (they pin the frame pointer
* across the region). This is the GDB-side fix; see elf_init_ehframe_gdb
* for details.
*/
static
void
elf_init_ehframe_perf
(
ELFObjectContext
*
ctx
) {
int
fde_ptr_enc
=
DWRF_EH_PE_pcrel
|
DWRF_EH_PE_sdata4
;
uint8_t
*
p
=
ctx
->
p
;
uint8_t
*
framep
=
p
;
// Remember start of frame data
/*
* DWARF Unwind Table for Trampoline Function
*
* This section defines DWARF Call Frame Information (CFI) using encoded macros
* like `DWRF_U8`, `DWRF_UV`, and `DWRF_SECTION` to describe how the trampoline function
* preserves and restores registers. This is used by profiling tools (e.g., `perf`)
* and debuggers for stack unwinding in JIT-compiled code.
*
* -------------------------------------------------
* TO REGENERATE THIS TABLE FROM GCC OBJECTS:
* -------------------------------------------------
*
* 1. Create a trampoline source file (e.g., `trampoline.c`):
*
* #include <Python.h>
* typedef PyObject* (*py_evaluator)(void*, void*, int);
* PyObject* trampoline(void *ts, void *f, int throwflag, py_evaluator evaluator) {
* return evaluator(ts, f, throwflag);
* }
*
* 2. Compile to an object file with frame pointer preservation:
*
* gcc trampoline.c -I. -I./Include -O2 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -c
*
* 3. Extract DWARF unwind info from the object file:
*
* readelf -w trampoline.o
*
* Example output from `.eh_frame`:
*
* 00000000 CIE
* Version: 1
* Augmentation: "zR"
* Code alignment factor: 4
* Data alignment factor: -8
* Return address column: 30
* DW_CFA_def_cfa: r31 (sp) ofs 0
*
* 00000014 FDE cie=00000000 pc=0..14
* DW_CFA_advance_loc: 4
* DW_CFA_def_cfa_offset: 16
* DW_CFA_offset: r29 at cfa-16
* DW_CFA_offset: r30 at cfa-8
* DW_CFA_advance_loc: 12
* DW_CFA_restore: r30
* DW_CFA_restore: r29
* DW_CFA_def_cfa_offset: 0
*
* -- These values can be verified by comparing with `readelf -w` or `llvm-dwarfdump --eh-frame`.
*
* ----------------------------------
* HOW TO TRANSLATE TO DWRF_* MACROS:
* ----------------------------------
*
* After compiling your trampoline with:
*
* gcc trampoline.c -I. -I./Include -O2 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -c
*
* run:
*
* readelf -w trampoline.o
*
* to inspect the generated `.eh_frame` data. You will see two main components:
*
* 1. A CIE (Common Information Entry): shared configuration used by all FDEs.
* 2. An FDE (Frame Description Entry): function-specific unwind instructions.
*
* ---------------------
* Translating the CIE:
* ---------------------
* From `readelf -w`, you might see:
*
* 00000000 0000000000000010 00000000 CIE
* Version: 1
* Augmentation: "zR"
* Code alignment factor: 4
* Data alignment factor: -8
* Return address column: 30
* Augmentation data: 1b
* DW_CFA_def_cfa: r31 (sp) ofs 0
*
* Map this to:
*
* DWRF_SECTION(CIE,
* DWRF_U32(0); // CIE ID (always 0 for CIEs)
* DWRF_U8(DWRF_CIE_VERSION); // Version: 1
* DWRF_STR("zR"); // Augmentation string "zR"
* DWRF_UV(4); // Code alignment factor = 4
* DWRF_SV(-8); // Data alignment factor = -8
* DWRF_U8(DWRF_REG_RA); // Return address register (e.g., x30 = 30)
* DWRF_UV(1); // Augmentation data length = 1
* DWRF_U8(DWRF_EH_PE_pcrel | DWRF_EH_PE_sdata4); // Encoding for FDE pointers
*
* DWRF_U8(DWRF_CFA_def_cfa); // DW_CFA_def_cfa
* DWRF_UV(DWRF_REG_SP); // Register: SP (r31)
* DWRF_UV(0); // Offset = 0
*
* DWRF_ALIGNNOP(sizeof(uintptr_t)); // Align to pointer size boundary
* )
*
* Notes:
* - Use `DWRF_UV` for unsigned LEB128, `DWRF_SV` for signed LEB128.
* - `DWRF_REG_RA` and `DWRF_REG_SP` are architecture-defined constants.
*
* ---------------------
* Translating the FDE:
* ---------------------
* From `readelf -w`:
*
* 00000014 0000000000000020 00000018 FDE cie=00000000 pc=0000000000000000..0000000000000014
* DW_CFA_advance_loc: 4
* DW_CFA_def_cfa_offset: 16
* DW_CFA_offset: r29 at cfa-16
* DW_CFA_offset: r30 at cfa-8
* DW_CFA_advance_loc: 12
* DW_CFA_restore: r30
* DW_CFA_restore: r29
* DW_CFA_def_cfa_offset: 0
*
* Map the FDE header and instructions to:
*
* DWRF_SECTION(FDE,
* DWRF_U32((uint32_t)(p - framep)); // Offset to CIE (relative from here)
* DWRF_U32(pc_relative_offset); // PC-relative location of the code (calculated dynamically)
* DWRF_U32(ctx->code_size); // Code range covered by this FDE
* DWRF_U8(0); // Augmentation data length (none)
*
* DWRF_U8(DWRF_CFA_advance_loc | 1); // Advance location by 1 unit (1 * 4 = 4 bytes)
* DWRF_U8(DWRF_CFA_def_cfa_offset); // CFA = SP + 16
* DWRF_UV(16);
*
* DWRF_U8(DWRF_CFA_offset | DWRF_REG_FP); // Save x29 (frame pointer)
* DWRF_UV(2); // At offset 2 * 8 = 16 bytes
*
* DWRF_U8(DWRF_CFA_offset | DWRF_REG_RA); // Save x30 (return address)
* DWRF_UV(1); // At offset 1 * 8 = 8 bytes
*
* DWRF_U8(DWRF_CFA_advance_loc | 3); // Advance location by 3 units (3 * 4 = 12 bytes)
*
* DWRF_U8(DWRF_CFA_offset | DWRF_REG_RA); // Restore x30
* DWRF_U8(DWRF_CFA_offset | DWRF_REG_FP); // Restore x29
*
* DWRF_U8(DWRF_CFA_def_cfa_offset); // CFA = SP
* DWRF_UV(0);
* )
*
* To regenerate:
* 1. Get the `code alignment factor`, `data alignment factor`, and `RA column` from the CIE.
* 2. Note the range of the function from the FDE's `pc=...` line and map it to the JIT code as
* the code is in a different address space every time.
* 3. For each `DW_CFA_*` entry, use the corresponding `DWRF_*` macro:
* - `DW_CFA_def_cfa_offset` → DWRF_U8(DWRF_CFA_def_cfa_offset), DWRF_UV(value)
* - `DW_CFA_offset: rX` → DWRF_U8(DWRF_CFA_offset | reg), DWRF_UV(offset)
* - `DW_CFA_restore: rX` → DWRF_U8(DWRF_CFA_offset | reg) // restore is same as reusing offset
* - `DW_CFA_advance_loc: N` → DWRF_U8(DWRF_CFA_advance_loc | (N / code_alignment_factor))
* 4. Use `DWRF_REG_FP`, `DWRF_REG_RA`, etc., for register numbers.
* 5. Use `sizeof(uintptr_t)` (typically 8) for pointer size calculations and alignment.
*/
/*
* Emit DWARF EH CIE (Common Information Entry)
*
* The CIE describes the calling conventions and basic unwinding rules
* that apply to all functions in this compilation unit.
*/
DWRF_SECTION
(
CIE
,
DWRF_U32
(
0
);
// CIE ID (0 indicates this is a CIE)
DWRF_U8
(
DWRF_CIE_VERSION
);
// CIE version (1)
DWRF_STR
(
"zR"
);
// Augmentation string ("zR" = has LSDA)
#ifdef
__x86_64__
DWRF_UV
(
1
);
// Code alignment factor (x86_64: 1 byte)
#elif
defined(
__aarch64__
)
&&
defined(
__AARCH64EL__
)
&&
!defined(
__ILP32__
)
DWRF_UV
(
4
);
// Code alignment factor (AArch64: 4 bytes per instruction)
#endif
DWRF_SV
(
-
(
int64_t
)
sizeof
(
uintptr_t
));
// Data alignment factor (negative)
DWRF_U8
(
DWRF_REG_RA
);
// Return address register number
DWRF_UV
(
1
);
// Augmentation data length
DWRF_U8
(
fde_ptr_enc
);
// FDE pointer encoding
/* Initial CFI instructions - describe default calling convention */
#ifdef
__x86_64__
/* x86_64 initial CFI state */
DWRF_U8
(
DWRF_CFA_def_cfa
);
// Define CFA (Call Frame Address)
DWRF_UV
(
DWRF_REG_SP
);
// CFA = SP register
DWRF_UV
(
sizeof
(
uintptr_t
));
// CFA = SP + pointer_size
DWRF_U8
(
DWRF_CFA_offset
|
DWRF_REG_RA
);
// Return address is saved
DWRF_UV
(
1
);
// At offset 1 from CFA
#elif
defined(
__aarch64__
)
&&
defined(
__AARCH64EL__
)
&&
!defined(
__ILP32__
)
/* AArch64 initial CFI state */
DWRF_U8
(
DWRF_CFA_def_cfa
);
// Define CFA (Call Frame Address)
DWRF_UV
(
DWRF_REG_SP
);
// CFA = SP register
DWRF_UV
(
0
);
// CFA = SP + 0 (AArch64 starts with offset 0)
// No initial register saves in AArch64 CIE
#endif
DWRF_ALIGNNOP
(
sizeof
(
uintptr_t
));
// Align to pointer boundary
)
/*
* Emit DWARF EH FDE (Frame Description Entry)
*
* The FDE describes unwinding information specific to this function.
* It references the CIE and provides function-specific CFI instructions.
*
* The PC-relative offset is calculated after the entire EH frame is built
* to ensure accurate positioning relative to the synthesized DSO layout.
*/
DWRF_SECTION
(
FDE
,
DWRF_U32
((
uint32_t
)(
p
-
framep
));
// Offset to CIE (backwards reference)
/*
* In perf jitdump mode the FDE PC field is encoded PC-relative and
* points back to code_start. Record where that field lives so we can
* patch in the final offset after the rest of the synthetic DSO
* layout is known.
*/
ctx
->
fde_p
=
p
;
// Remember where PC offset field is located for later calculation
DWRF_U32
(
0
);
// Placeholder for PC-relative offset (calculated below)
DWRF_U32
(
ctx
->
code_size
);
// Address range covered by this FDE (code length)
DWRF_U8
(
0
);
// Augmentation data length (none)
/*
* Architecture-specific CFI instructions
*
* These instructions describe how registers are saved and restored
* during function calls. Each architecture has different calling
* conventions and register usage patterns.
*/
#ifdef
__x86_64__
/* x86_64 calling convention unwinding rules */
# if
defined(
__CET__
)
&&
(
__CET__
&
1
)
DWRF_U8
(
DWRF_CFA_advance_loc
|
4
);
// Advance past endbr64 (4 bytes)
# endif
DWRF_U8
(
DWRF_CFA_advance_loc
|
1
);
// Advance past push %rbp (1 byte)
DWRF_U8
(
DWRF_CFA_def_cfa_offset
);
// def_cfa_offset 16
DWRF_UV
(
16
);
// New offset: SP + 16
DWRF_U8
(
DWRF_CFA_offset
|
DWRF_REG_BP
);
// offset r6 at cfa-16
DWRF_UV
(
2
);
// Offset factor: 2 * 8 = 16 bytes
DWRF_U8
(
DWRF_CFA_advance_loc
|
3
);
// Advance past mov %rsp,%rbp (3 bytes)
DWRF_U8
(
DWRF_CFA_def_cfa_register
);
// def_cfa_register r6
DWRF_UV
(
DWRF_REG_BP
);
// Use base pointer register
DWRF_U8
(
DWRF_CFA_advance_loc
|
3
);
// Advance past call *%rcx (2 bytes) + pop %rbp (1 byte) = 3
DWRF_U8
(
DWRF_CFA_def_cfa
);
// def_cfa r7 ofs 8
DWRF_UV
(
DWRF_REG_SP
);
// Use stack pointer register
DWRF_UV
(
8
);
// New offset: SP + 8
#elif
defined(
__aarch64__
)
&&
defined(
__AARCH64EL__
)
&&
!defined(
__ILP32__
)
/* AArch64 calling convention unwinding rules */
#if
defined(
__ARM_FEATURE_PAC_DEFAULT
)
||
\
(defined(
__ARM_FEATURE_BTI_DEFAULT
)
&&
__ARM_FEATURE_BTI_DEFAULT
==
1
)
DWRF_U8
(
DWRF_CFA_advance_loc
|
1
);
// Advance past SIGN_LR (4 bytes)
#endif
#if
defined(
__ARM_FEATURE_PAC_DEFAULT
)
DWRF_U8
(
DWRF_CFA_AARCH64_negate_ra_state
);
// Saved LR is PAC-signed from here
#endif
DWRF_U8
(
DWRF_CFA_advance_loc
|
1
);
// Advance by 1 instruction (4 bytes)
DWRF_U8
(
DWRF_CFA_def_cfa_offset
);
// CFA = SP + 16
DWRF_UV
(
16
);
// Stack pointer moved by 16 bytes
DWRF_U8
(
DWRF_CFA_offset
|
DWRF_REG_FP
);
// x29 (frame pointer) saved
DWRF_UV
(
2
);
// At CFA-16 (2 * 8 = 16 bytes from CFA)
DWRF_U8
(
DWRF_CFA_offset
|
DWRF_REG_RA
);
// x30 (link register) saved
DWRF_UV
(
1
);
// At CFA-8 (1 * 8 = 8 bytes from CFA)
DWRF_U8
(
DWRF_CFA_advance_loc
|
3
);
// Advance by 3 instructions (12 bytes)
#if
defined(
__ARM_FEATURE_PAC_DEFAULT
)
DWRF_U8
(
DWRF_CFA_AARCH64_negate_ra_state
);
// LR is authenticated, no longer PAC-signed
#endif
DWRF_U8
(
DWRF_CFA_def_cfa_register
);
// CFA = FP (x29) + 16
DWRF_UV
(
DWRF_REG_FP
);
DWRF_U8
(
DWRF_CFA_restore
|
DWRF_REG_RA
);
// Restore x30 - NO DWRF_UV() after this!
DWRF_U8
(
DWRF_CFA_restore
|
DWRF_REG_FP
);
// Restore x29 - NO DWRF_UV() after this!
DWRF_U8
(
DWRF_CFA_def_cfa
);
// CFA = SP + 0 (stack restored)
DWRF_UV
(
DWRF_REG_SP
);
DWRF_UV
(
0
);
#else
# error
"Unsupported target architecture"
#endif
DWRF_ALIGNNOP
(
sizeof
(
uintptr_t
));
// Align to pointer boundary
)
ctx
->
p
=
p
;
// Update context pointer to end of generated data
/* Calculate and update the PC-relative offset in the FDE
*
* When perf processes the jitdump, it creates a synthesized DSO with this layout:
*
* Synthesized DSO Memory Layout:
* ┌─────────────────────────────────────────────────────────────┐ < code_start
* │ Code Section │
* │ (round_up(code_size, 8) bytes) │
* ├─────────────────────────────────────────────────────────────┤ < start of EH frame data
* │ EH Frame Data │
* │ ┌─────────────────────────────────────────────────────┐ │
* │ │ CIE data │ │
* │ └─────────────────────────────────────────────────────┘ │
* │ ┌─────────────────────────────────────────────────────┐ │
* │ │ FDE Header: │ │
* │ │ - CIE offset (4 bytes) │ │
* │ │ - PC offset (4 bytes) <─ fde_offset_in_frame ─────┼────┼─> points to code_start
* │ │ - address range (4 bytes) │ │ (this specific field)
* │ │ CFI Instructions... │ │
* │ └─────────────────────────────────────────────────────┘ │
* ├─────────────────────────────────────────────────────────────┤ < reference_point
* │ EhFrameHeader │
* │ (navigation metadata) │
* └─────────────────────────────────────────────────────────────┘
*
* The PC offset field in the FDE must contain the distance from itself to code_start:
*
* distance = code_start - fde_pc_field
*
* Where:
* fde_pc_field_location = reference_point - eh_frame_size + fde_offset_in_frame
* code_start_location = reference_point - eh_frame_size - round_up(code_size, 8)
*
* Therefore:
* distance = code_start_location - fde_pc_field_location
* = (ref - eh_frame_size - rounded_code_size) - (ref - eh_frame_size + fde_offset_in_frame)
* = -rounded_code_size - fde_offset_in_frame
* = -(round_up(code_size, 8) + fde_offset_in_frame)
*
* Note: fde_offset_in_frame is the offset from EH frame start to the PC offset field.
*
*/
int32_t
rounded_code_size
=
(
int32_t
)
_Py_SIZE_ROUND_UP
(
ctx
->
code_size
,
8
);
int32_t
fde_offset_in_frame
=
(
int32_t
)(
ctx
->
fde_p
-
framep
);
*
(
int32_t
*
)
ctx
->
fde_p
=
-
(
rounded_code_size
+
fde_offset_in_frame
);
}
/*
* Build .eh_frame data for the GDB JIT interface.
*
* The executor runs inside the frame established by _PyJIT_Entry, but the
* synthetic executor FDE collapses that state into a single logical JIT frame
* that unwinds directly into _PyEval_*. Executor stencils never touch the
* frame pointer - enforced by Tools/jit/_optimizers.py _validate() and
* -mframe-pointer=reserved - so the steady-state rule is valid at every PC
* and the FDE body is empty. Tools/jit/_targets.py derives the initial CFI
* rules from the row active at the executor call in the compiled shim object.
*/
#if
defined(
PY_HAVE_JIT_GDB_UNWIND
)
static
void
elf_init_ehframe_gdb
(
ELFObjectContext
*
ctx
) {
int
fde_ptr_enc
=
DWRF_EH_PE_absptr
;
uint8_t
*
p
=
ctx
->
p
;
uint8_t
*
framep
=
p
;
DWRF_SECTION
(
CIE
,
DWRF_U32
(
0
);
// CIE ID
DWRF_U8
(
DWRF_CIE_VERSION
);
DWRF_STR
(
"zR"
);
// aug data length + FDE ptr encoding follow
DWRF_UV
(
JIT_UNWIND_CODE_ALIGNMENT_FACTOR
);
DWRF_SV
(
JIT_UNWIND_DATA_ALIGNMENT_FACTOR
);
DWRF_U8
(
JIT_UNWIND_RA_REG
);
DWRF_UV
(
1
);
// Augmentation data length
DWRF_U8
(
fde_ptr_enc
);
// FDE pointer encoding
/* Executor steady-state rule (our invariant, not the compiler's). */
DWRF_U8
(
DWRF_CFA_def_cfa
);
DWRF_UV
(
JIT_UNWIND_CFA_REG
);
DWRF_UV
(
JIT_UNWIND_CFA_OFFSET
);
DWRF_U8
(
DWRF_CFA_offset
|
JIT_UNWIND_FP_REG
);
DWRF_UV
(
JIT_UNWIND_FP_OFFSET
);
DWRF_U8
(
DWRF_CFA_offset
|
JIT_UNWIND_RA_REG
);
DWRF_UV
(
JIT_UNWIND_RA_OFFSET
);
DWRF_ALIGNNOP
(
sizeof
(
uintptr_t
));
)
DWRF_SECTION
(
FDE
,
DWRF_U32
((
uint32_t
)(
p
-
framep
));
// Offset to CIE (backwards reference)
DWRF_ADDR
(
ctx
->
code_addr
);
// Absolute code start
DWRF_ADDR
((
uintptr_t
)
ctx
->
code_size
);
// Code range covered
DWRF_U8
(
0
);
// Augmentation data length (none)
DWRF_ALIGNNOP
(
sizeof
(
uintptr_t
));
)
ctx
->
p
=
p
;
}
#endif
#if
defined(
PY_HAVE_JIT_GDB_UNWIND
)
enum
{
JIT_NOACTION
=
0
,
JIT_REGISTER_FN
=
1
,
JIT_UNREGISTER_FN
=
2
,
};
struct
jit_code_entry
{
struct
jit_code_entry
*
next
;
struct
jit_code_entry
*
prev
;
const
char
*
symfile_addr
;
uint64_t
symfile_size
;
const
void
*
code_addr
;
};
struct
jit_descriptor
{
uint32_t
version
;
uint32_t
action_flag
;
struct
jit_code_entry
*
relevant_entry
;
struct
jit_code_entry
*
first_entry
;
};
PyMutex
_Py_jit_debug_mutex
=
{
0
};
Py_EXPORTED_SYMBOL
volatile
struct
jit_descriptor
__jit_debug_descriptor
=
{
1
,
JIT_NOACTION
,
NULL
,
NULL
};
Py_EXPORTED_SYMBOL
void
__attribute__((
noinline
))
__jit_debug_register_code
(
void
)
{
/* Keep this call visible to debuggers and not optimized away. */
(
void
)
__jit_debug_descriptor
.
action_flag
;
#if
defined(
__GNUC__
)
||
defined(
__clang__
)
__asm__ __volatile__(
""
:::
"memory"
);
#endif
}
static
uint16_t
gdb_jit_machine_id
(
void
)
{
/* Map the current target to ELF e_machine; return 0 to skip registration. */
#if
defined(
__x86_64__
)
||
defined(
_M_X64
)
return
EM_X86_64
;
#elif
defined(
__aarch64__
)
&&
!defined(
__ILP32__
)
return
EM_AARCH64
;
#else
return
0
;
#endif
}
static
struct
jit_code_entry
*
gdb_jit_register_code
(
const
void
*
code_addr
,
size_t
code_size
,
const
char
*
symname
,
const
uint8_t
*
eh_frame
,
size_t
eh_frame_size
)
{
/*
* Build a minimal in-memory ELF for GDB's JIT interface and link it into
* __jit_debug_descriptor so debuggers can resolve JIT code.
*/
if
(
code_addr
==
NULL
||
code_size
==
0
||
symname
==
NULL
) {
return
NULL
;
}
const
uint16_t
machine
=
gdb_jit_machine_id
();
if
(
machine
==
0
) {
return
NULL
;
}
enum
{
SH_NULL
=
0
,
SH_TEXT
,
SH_EH_FRAME
,
SH_SHSTRTAB
,
SH_STRTAB
,
SH_SYMTAB
,
SH_NUM
,
};
static
const
char
shstrtab
[]
=
"\0.text\0.eh_frame\0.shstrtab\0.strtab\0.symtab"
;
_Static_assert
(
sizeof
(
shstrtab
)
==
1
+
sizeof
(
".text"
)
+
sizeof
(
".eh_frame"
)
+
sizeof
(
".shstrtab"
)
+
sizeof
(
".strtab"
)
+
sizeof
(
".symtab"
),
"shstrtab size mismatch"
);
const
size_t
shstrtab_size
=
sizeof
(
shstrtab
);
const
size_t
sh_text
=
1
;
const
size_t
sh_eh_frame
=
sh_text
+
sizeof
(
".text"
);
const
size_t
sh_shstrtab
=
sh_eh_frame
+
sizeof
(
".eh_frame"
);
const
size_t
sh_strtab
=
sh_shstrtab
+
sizeof
(
".shstrtab"
);
const
size_t
sh_symtab
=
sh_strtab
+
sizeof
(
".strtab"
);
const
size_t
text_size
=
code_size
;
const
size_t
text_padded
=
_Py_SIZE_ROUND_UP
(
text_size
,
8
);
const
size_t
strtab_size
=
1
+
strlen
(
symname
)
+
1
;
const
size_t
symtab_size
=
3
*
sizeof
(
Elf64_Sym
);
size_t
offset
=
sizeof
(
Elf64_Ehdr
);
offset
=
_Py_SIZE_ROUND_UP
(
offset
,
16
);
const
size_t
text_off
=
offset
;
const
size_t
eh_off
=
text_off
+
text_padded
;
offset
=
eh_off
+
eh_frame_size
;
const
size_t
shstr_off
=
offset
;
offset
+=
shstrtab_size
;
const
size_t
str_off
=
offset
;
offset
+=
strtab_size
;
/* Elf64_Sym requires 8-byte alignment for st_value/st_size. */
offset
=
_Py_SIZE_ROUND_UP
(
offset
,
8
);
const
size_t
sym_off
=
offset
;
offset
+=
symtab_size
;
offset
=
_Py_SIZE_ROUND_UP
(
offset
,
sizeof
(
Elf64_Shdr
));
const
size_t
sh_off
=
offset
;
const
size_t
shnum
=
SH_NUM
;
const
size_t
total_size
=
sh_off
+
shnum
*
sizeof
(
Elf64_Shdr
);
uint8_t
*
buf
=
(
uint8_t
*
)
PyMem_RawMalloc
(
total_size
);
if
(
buf
==
NULL
) {
return
NULL
;
}
memset
(
buf
,
0
,
total_size
);
Elf64_Ehdr
*
ehdr
=
(
Elf64_Ehdr
*
)
buf
;
memcpy
(
ehdr
->
e_ident
,
ELFMAG
,
SELFMAG
);
ehdr
->
e_ident
[
EI_CLASS
]
=
ELFCLASS64
;
ehdr
->
e_ident
[
EI_DATA
]
=
ELFDATA2LSB
;
ehdr
->
e_ident
[
EI_VERSION
]
=
EV_CURRENT
;
ehdr
->
e_ident
[
EI_OSABI
]
=
ELFOSABI_NONE
;
ehdr
->
e_type
=
ET_DYN
;
ehdr
->
e_machine
=
machine
;
ehdr
->
e_version
=
EV_CURRENT
;
ehdr
->
e_entry
=
0
;
ehdr
->
e_phoff
=
0
;
ehdr
->
e_shoff
=
sh_off
;
ehdr
->
e_ehsize
=
sizeof
(
Elf64_Ehdr
);
ehdr
->
e_shentsize
=
sizeof
(
Elf64_Shdr
);
ehdr
->
e_shnum
=
shnum
;
ehdr
->
e_shstrndx
=
SH_SHSTRTAB
;
memcpy
(
buf
+
text_off
,
code_addr
,
text_size
);
memcpy
(
buf
+
eh_off
,
eh_frame
,
eh_frame_size
);
char
*
shstr
=
(
char
*
)(
buf
+
shstr_off
);
memcpy
(
shstr
,
shstrtab
,
shstrtab_size
);
char
*
strtab
=
(
char
*
)(
buf
+
str_off
);
strtab
[
0
]
=
'\0'
;
memcpy
(
strtab
+
1
,
symname
,
strlen
(
symname
));
strtab
[
strtab_size
-
1
]
=
'\0'
;
Elf64_Sym
*
syms
=
(
Elf64_Sym
*
)(
buf
+
sym_off
);
memset
(
syms
,
0
,
symtab_size
);
/* Section symbol for .text (local) */
syms
[
1
].
st_info
=
ELF64_ST_INFO
(
STB_LOCAL
,
STT_SECTION
);
syms
[
1
].
st_shndx
=
1
;
/* Function symbol */
syms
[
2
].
st_name
=
1
;
syms
[
2
].
st_info
=
ELF64_ST_INFO
(
STB_GLOBAL
,
STT_FUNC
);
syms
[
2
].
st_other
=
STV_DEFAULT
;
syms
[
2
].
st_shndx
=
1
;
/* For ET_DYN/ET_EXEC, st_value is the absolute virtual address. */
syms
[
2
].
st_value
=
(
Elf64_Addr
)(
uintptr_t
)
code_addr
;
syms
[
2
].
st_size
=
code_size
;
Elf64_Shdr
*
shdrs
=
(
Elf64_Shdr
*
)(
buf
+
sh_off
);
memset
(
shdrs
,
0
,
shnum
*
sizeof
(
Elf64_Shdr
));
shdrs
[
SH_TEXT
].
sh_name
=
sh_text
;
shdrs
[
SH_TEXT
].
sh_type
=
SHT_PROGBITS
;
shdrs
[
SH_TEXT
].
sh_flags
=
SHF_ALLOC
|
SHF_EXECINSTR
;
shdrs
[
SH_TEXT
].
sh_addr
=
(
Elf64_Addr
)(
uintptr_t
)
code_addr
;
shdrs
[
SH_TEXT
].
sh_offset
=
text_off
;
shdrs
[
SH_TEXT
].
sh_size
=
text_size
;
shdrs
[
SH_TEXT
].
sh_addralign
=
16
;
shdrs
[
SH_EH_FRAME
].
sh_name
=
sh_eh_frame
;
shdrs
[
SH_EH_FRAME
].
sh_type
=
SHT_PROGBITS
;
shdrs
[
SH_EH_FRAME
].
sh_flags
=
SHF_ALLOC
;
shdrs
[
SH_EH_FRAME
].
sh_addr
=
(
Elf64_Addr
)((
uintptr_t
)
code_addr
+
text_padded
);
shdrs
[
SH_EH_FRAME
].
sh_offset
=
eh_off
;
shdrs
[
SH_EH_FRAME
].
sh_size
=
eh_frame_size
;
shdrs
[
SH_EH_FRAME
].
sh_addralign
=
8
;
shdrs
[
SH_SHSTRTAB
].
sh_name
=
sh_shstrtab
;
shdrs
[
SH_SHSTRTAB
].
sh_type
=
SHT_STRTAB
;
shdrs
[
SH_SHSTRTAB
].
sh_offset
=
shstr_off
;
shdrs
[
SH_SHSTRTAB
].
sh_size
=
shstrtab_size
;
shdrs
[
SH_SHSTRTAB
].
sh_addralign
=
1
;
shdrs
[
SH_STRTAB
].
sh_name
=
sh_strtab
;
shdrs
[
SH_STRTAB
].
sh_type
=
SHT_STRTAB
;
shdrs
[
SH_STRTAB
].
sh_offset
=
str_off
;
shdrs
[
SH_STRTAB
].
sh_size
=
strtab_size
;
shdrs
[
SH_STRTAB
].
sh_addralign
=
1
;
shdrs
[
SH_SYMTAB
].
sh_name
=
sh_symtab
;
shdrs
[
SH_SYMTAB
].
sh_type
=
SHT_SYMTAB
;
shdrs
[
SH_SYMTAB
].
sh_offset
=
sym_off
;
shdrs
[
SH_SYMTAB
].
sh_size
=
symtab_size
;
shdrs
[
SH_SYMTAB
].
sh_link
=
SH_STRTAB
;
shdrs
[
SH_SYMTAB
].
sh_info
=
2
;
shdrs
[
SH_SYMTAB
].
sh_addralign
=
8
;
shdrs
[
SH_SYMTAB
].
sh_entsize
=
sizeof
(
Elf64_Sym
);
struct
jit_code_entry
*
entry
=
PyMem_RawMalloc
(
sizeof
(
*
entry
));
if
(
entry
==
NULL
) {
PyMem_RawFree
(
buf
);
return
NULL
;
}
entry
->
symfile_addr
=
(
const
char
*
)
buf
;
entry
->
symfile_size
=
total_size
;
entry
->
code_addr
=
code_addr
;
PyMutex_Lock
(
&
_Py_jit_debug_mutex
);
entry
->
prev
=
NULL
;
entry
->
next
=
__jit_debug_descriptor
.
first_entry
;
if
(
entry
->
next
!=
NULL
) {
entry
->
next
->
prev
=
entry
;
}
__jit_debug_descriptor
.
first_entry
=
entry
;
__jit_debug_descriptor
.
relevant_entry
=
entry
;
__jit_debug_descriptor
.
action_flag
=
JIT_REGISTER_FN
;
__jit_debug_register_code
();
__jit_debug_descriptor
.
action_flag
=
JIT_NOACTION
;
__jit_debug_descriptor
.
relevant_entry
=
NULL
;
PyMutex_Unlock
(
&
_Py_jit_debug_mutex
);
return
entry
;
}
#endif
// defined(PY_HAVE_JIT_GDB_UNWIND)
void
*
_PyJitUnwind_GdbRegisterCode
(
const
void
*
code_addr
,
size_t
code_size
,
const
char
*
entry
,
const
char
*
filename
)
{
#if
defined(
PY_HAVE_JIT_GDB_UNWIND
)
/* GDB expects a stable symbol name and absolute addresses in .eh_frame. */
if
(
entry
==
NULL
) {
entry
=
""
;
}
if
(
filename
==
NULL
) {
filename
=
""
;
}
size_t
name_size
=
snprintf
(
NULL
,
0
,
"py::%s:%s"
,
entry
,
filename
)
+
1
;
char
*
name
=
(
char
*
)
PyMem_RawMalloc
(
name_size
);
if
(
name
==
NULL
) {
return
NULL
;
}
snprintf
(
name
,
name_size
,
"py::%s:%s"
,
entry
,
filename
);
uint8_t
buffer
[
1024
];
size_t
eh_frame_size
=
_PyJitUnwind_BuildEhFrame
(
buffer
,
sizeof
(
buffer
),
code_addr
,
code_size
,
1
);
if
(
eh_frame_size
==
0
) {
PyMem_RawFree
(
name
);
return
NULL
;
}
void
*
handle
=
gdb_jit_register_code
(
code_addr
,
code_size
,
name
,
buffer
,
eh_frame_size
);
PyMem_RawFree
(
name
);
return
handle
;
#else
(
void
)
code_addr
;
(
void
)
code_size
;
(
void
)
entry
;
(
void
)
filename
;
return
NULL
;
#endif
}
void
_PyJitUnwind_GdbUnregisterCode
(
void
*
handle
)
{
#if
defined(
PY_HAVE_JIT_GDB_UNWIND
)
struct
jit_code_entry
*
entry
=
(
struct
jit_code_entry
*
)
handle
;
if
(
entry
==
NULL
) {
return
;
}
PyMutex_Lock
(
&
_Py_jit_debug_mutex
);
if
(
entry
->
prev
!=
NULL
) {
entry
->
prev
->
next
=
entry
->
next
;
}
else
{
__jit_debug_descriptor
.
first_entry
=
entry
->
next
;
}
if
(
entry
->
next
!=
NULL
) {
entry
->
next
->
prev
=
entry
->
prev
;
}
__jit_debug_descriptor
.
relevant_entry
=
entry
;
__jit_debug_descriptor
.
action_flag
=
JIT_UNREGISTER_FN
;
__jit_debug_register_code
();
__jit_debug_descriptor
.
action_flag
=
JIT_NOACTION
;
__jit_debug_descriptor
.
relevant_entry
=
NULL
;
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