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| author | Jameson Nash <vtjnash@gmail.com> | 2020-12-16 12:36:38 -0500 |
|---|---|---|
| committer | Dave Watson <dade.watson@gmail.com> | 2021-02-17 09:13:13 -0800 |
| commit | d21f565432686032b3d534e5ccaac56a3a454eef (patch) | |
| tree | a1b7f1f48ad4651883ec93a5cdb7cb06608d1067 | |
| parent | 4407cf07d53de767c2a2b8297eaea00ce33ccd32 (diff) | |
| download | libunwind-d21f565432686032b3d534e5ccaac56a3a454eef.tar.gz | |
improve unw_getcontext on ARM/Thumb
Better support unw_resume, by returning r0 from the user, instead of
hard-coding it to zero (also incidentally fixing a compiler warning
about an unused expression). This better mimics a real function call,
instead of hard-coding the return value. When in thumb mode, this also
means we also need to avoid switching between thumb and ARM upon return
to this point, so we need to set the pc accurately to point after the
return instruction. When in ARM mode, we need an extra nop also to point
at the correct return instruction (since the stored value of pc in the
context runs ahead by 8 bytes, while stmia is only 4 bytes).
| -rw-r--r-- | include/libunwind-arm.h | 52 |
1 files changed, 33 insertions, 19 deletions
diff --git a/include/libunwind-arm.h b/include/libunwind-arm.h index 1a6c6b6d..80f87c07 100644 --- a/include/libunwind-arm.h +++ b/include/libunwind-arm.h @@ -268,28 +268,42 @@ typedef struct unw_tdep_context } unw_tdep_context_t; -/* There is no getcontext() on ARM. Use a stub version which only saves GP - registers. FIXME: Not ideal, may not be sufficient for all libunwind - use cases. Stores pc+8, which is only approximately correct, really. */ +/* FIXME: this is a stub version which only saves GP registers. Not ideal, but + may be sufficient for all libunwind use cases. + In thumb mode, we return directly back to thumb mode on return (with bx), to + avoid altering any registers after unw_resume. */ #ifndef __thumb__ -#define unw_tdep_getcontext(uc) (({ \ - unw_tdep_context_t *unw_ctx = (uc); \ - register unsigned long *unw_base __asm__ ("r0") = unw_ctx->regs; \ - __asm__ __volatile__ ( \ - "stmia %[base], {r0-r15}" \ - : : [base] "r" (unw_base) : "memory"); \ - }), 0) +#define unw_tdep_getcontext(uc) ({ \ + unw_tdep_context_t *unw_ctx = (uc); \ + register unsigned long *r0 __asm__ ("r0"); \ + unsigned long *unw_base = unw_ctx->regs; \ + __asm__ __volatile__ ( \ + "mov r0, #0\n" \ + "stmia %[base], {r0-r15}\n" \ + "nop\n" /* align return address to value stored by stmia */ \ + : [r0] "=r" (r0) : [base] "r" (unw_base) : "memory"); \ + (int)r0; }) #else /* __thumb__ */ -#define unw_tdep_getcontext(uc) (({ \ - unw_tdep_context_t *unw_ctx = (uc); \ - register unsigned long *unw_base __asm__ ("r0") = unw_ctx->regs; \ - __asm__ __volatile__ ( \ - ".align 2\nbx pc\nnop\n.code 32\n" \ - "stmia %[base], {r0-r15}\n" \ - "orr %[base], pc, #1\nbx %[base]\n" \ +#define unw_tdep_getcontext(uc) ({ \ + unw_tdep_context_t *unw_ctx = (uc); \ + register unsigned long *r0 __asm__ ("r0"); \ + unsigned long *unw_base = unw_ctx->regs; \ + __asm__ __volatile__ ( \ + ".align 2\n" \ + "bx pc\n" \ + "nop\n" \ + ".code 32\n" \ + "mov r0, #0\n" \ + "stmia %[base], {r0-r14}\n" \ + "adr r0, ret%=+1\n" \ + "str r0, [%[base], #60]\n" \ + "orr r0, pc, #1\n" \ + "bx r0\n" \ ".code 16\n" \ - : [base] "+r" (unw_base) : : "memory", "cc"); \ - }), 0) + "mov r0, #0\n" \ + "ret%=:\n" \ + : [r0] "=r" (r0) : [base] "r" (unw_base) : "memory", "cc"); \ + (int)r0; }) #endif #include "libunwind-dynamic.h" |