[libunwind] [libunwind] Add initial ARM64EC support (PR #138583)
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Mon May 5 13:47:45 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libunwind
Author: Jacek Caban (cjacek)
<details>
<summary>Changes</summary>
ARM64EC defines `__x86_64__`, which is sufficient to make most C/C++ code behave correctly. To preserve an external ABI compatible with x86_64, this patch uses the x86_64 context layout and implements `unw_getcontext` by storing the appropriate aarch64 registers according to the mapping defined by the ARM64EC ABI.
---
Full diff: https://github.com/llvm/llvm-project/pull/138583.diff
2 Files Affected:
- (modified) libunwind/src/UnwindRegistersRestore.S (+1-1)
- (modified) libunwind/src/UnwindRegistersSave.S (+49)
``````````diff
diff --git a/libunwind/src/UnwindRegistersRestore.S b/libunwind/src/UnwindRegistersRestore.S
index 1702d016c368b..5e199188945df 100644
--- a/libunwind/src/UnwindRegistersRestore.S
+++ b/libunwind/src/UnwindRegistersRestore.S
@@ -66,7 +66,7 @@ DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_x86_jumpto)
# skip fs
# skip gs
-#elif defined(__x86_64__)
+#elif defined(__x86_64__) && !defined(__arm64ec__)
DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_x86_64_jumpto)
#
diff --git a/libunwind/src/UnwindRegistersSave.S b/libunwind/src/UnwindRegistersSave.S
index a489a8ba6df15..12fd81d49299b 100644
--- a/libunwind/src/UnwindRegistersSave.S
+++ b/libunwind/src/UnwindRegistersSave.S
@@ -65,6 +65,53 @@ DEFINE_LIBUNWIND_FUNCTION(__unw_getcontext)
xorl %eax, %eax # return UNW_ESUCCESS
ret
+#elif defined(__arm64ec__)
+
+//
+// extern int __unw_getcontext(unw_context_t* thread_state)
+//
+// On entry:
+// thread_state pointer is in x0
+//
+ .section .text,"xr",discard,"#__unw_getcontext"
+ .p2align 2
+DEFINE_LIBUNWIND_FUNCTION("#__unw_getcontext")
+ stp x8, x27, [x0, #0x000] // rax, rbx
+ stp x0, x1, [x0, #0x010] // rcx, rdx
+ stp x26,x25, [x0, #0x020] // rdi, rsi
+ mov x1, sp
+ stp fp, x1, [x0, #0x030] // rbp, rsp
+ stp x2, x3, [x0, #0x040] // r8, r9
+ stp x4, x5, [x0, #0x050] // r10, r11
+ stp x19,x20, [x0, #0x060] // r12, r13
+ stp x21,x22, [x0, #0x070] // r14, r15
+ str x30, [x0, #0x080] // store return address as pc
+ stp q0, q1, [x0, #0x0b0] // xmm0, xmm1
+ stp q2, q3, [x0, #0x0d0] // xmm2, xmm3
+ stp q4, q5, [x0, #0x0f0] // xmm4, xmm5
+ stp q6, q7, [x0, #0x110] // xmm6, xmm7
+ stp q8, q9, [x0, #0x130] // xmm8, xmm9
+ stp q10,q11, [x0, #0x150] // xmm10,xmm11
+ stp q12,q13, [x0, #0x170] // xmm12,xmm13
+ stp q14,q15, [x0, #0x190] // xmm14,xmm15
+ mov x0, #0 // return UNW_ESUCCESS
+ ret
+
+ .globl "#unw_getcontext"
+ .set "#unw_getcontext", "#__unw_getcontext"
+ .weak_anti_dep __unw_getcontext
+ .set __unw_getcontext, "#__unw_getcontext"
+ .weak_anti_dep unw_getcontext
+ .set unw_getcontext, "#unw_getcontext"
+
+ .section .hybmp$x,"yi"
+ .symidx "#__unw_getcontext"
+ .symidx $ientry_thunk$cdecl$i8$i8
+ .word 1
+ .text
+
+ EXPORT_SYMBOL(unw_getcontext)
+
#elif defined(__x86_64__)
#
@@ -1181,7 +1228,9 @@ DEFINE_LIBUNWIND_FUNCTION(__unw_getcontext)
#endif
+#ifndef __arm64ec__
WEAK_ALIAS(__unw_getcontext, unw_getcontext)
+#endif
#endif /* !defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__wasm__) */
``````````
</details>
https://github.com/llvm/llvm-project/pull/138583
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