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Rework inline aarch64 asm for setcontext #748

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Jun 11, 2024
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Rework inline aarch64 asm for setcontext #748

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115 changes: 61 additions & 54 deletions src/aarch64/Gos-linux.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
Copyright (C) 2008 CodeSourcery
Copyright (C) 2011-2013 Linaro Limited
Copyright (C) 2012 Tommi Rantala <tt.rantala@gmail.com>
Copyright 2024 Stephen M. Webb <swebb@blackberry.com>

This file is part of libunwind.

Expand All @@ -28,6 +29,28 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */

#ifndef UNW_REMOTE_ONLY

/* Magic constants generated from gen-offsets.c */
#define SC_R0_OFF "8"
#define SC_R2_OFF "24"
#define SC_R18_OFF "152"
#define SC_R20_OFF "168"
#define SC_R22_OFF "184"
#define SC_R24_OFF "200"
#define SC_R26_OFF "216"
#define SC_R28_OFF "232"
#define SC_R30_OFF "248"

#define FP_R08_OFF "80"
#define FP_R09_OFF "88"
#define FP_R10_OFF "96"
#define FP_R11_OFF "104"
#define FP_R12_OFF "112"
#define FP_R13_OFF "120"
#define FP_R14_OFF "128"
#define FP_R15_OFF "136"

#define SC_SP_OFF "0x100"

HIDDEN int
aarch64_local_resume (unw_addr_space_t as, unw_cursor_t *cursor, void *arg)
{
Expand All @@ -36,65 +59,49 @@ aarch64_local_resume (unw_addr_space_t as, unw_cursor_t *cursor, void *arg)

if (c->sigcontext_format == AARCH64_SCF_NONE)
{

/*
* This is effectively the old POSIX setcontext().
*
* This inline asm is broken up to use local scratch registers for the
* uc_mcontext.regs and FPCTX base addresses because newer versions of GCC
* and clang barf on too many constraints (gh-702) when the C array
* elements are used directly.
*
* Clobbers aren't required for the inline asm because they just convince
* the compiler to save those registers and they never get restored
* becauise the asm ends with a plain ol' ret.
*/
register void* uc_mcontext __asm__ ("x5") = (void*) &uc->uc_mcontext;
register void* fpctx __asm__ ("x4") = (void*) GET_FPCTX(uc);

/* Since there are no signals involved here we restore EH and non scratch
registers only. */
__asm__ __volatile__ (
"ldr x0, %[x0]\n\t"
"ldr x1, %[x1]\n\t"
"ldr x2, %[x2]\n\t"
"ldr x3, %[x3]\n\t"
"ldr x19, %[x19]\n\t"
"ldr x20, %[x20]\n\t"
"ldr x21, %[x21]\n\t"
"ldr x22, %[x22]\n\t"
"ldr x23, %[x23]\n\t"
"ldr x24, %[x24]\n\t"
"ldr x25, %[x25]\n\t"
"ldr x26, %[x26]\n\t"
"ldr x27, %[x27]\n\t"
"ldr x28, %[x28]\n\t"
"ldr x29, %[x29]\n\t"
"ldr x30, %[x30]\n\t"
"ldr d8, %[d8]\n\t"
"ldr d9, %[d9]\n\t"
"ldr d10, %[d10]\n\t"
"ldr d11, %[d11]\n\t"
"ldr d12, %[d12]\n\t"
"ldr d13, %[d13]\n\t"
"ldr d14, %[d14]\n\t"
"ldr d15, %[d15]\n\t"
"ldr x5, %[sp]\n\t"
"ldp x0, x1, [x5, " SC_R0_OFF "]\n\t"
"ldp x2, x3, [x5, " SC_R2_OFF "]\n\t"
"ldp x18, x19, [x5, " SC_R18_OFF "]\n\t"
"ldp x20, x21, [x5, " SC_R20_OFF "]\n\t"
"ldp x22, x23, [x5, " SC_R22_OFF "]\n\t"
"ldp x24, x25, [x5, " SC_R24_OFF "]\n\t"
"ldp x26, x27, [x5, " SC_R26_OFF "]\n\t"
"ldp x28, x29, [x5, " SC_R28_OFF "]\n\t"
"ldr x30, [x5, " SC_R30_OFF "]\n\t"
"ldr d8, [x4, " FP_R08_OFF "]\n\t"
"ldr d9, [x4, " FP_R09_OFF "]\n\t"
"ldr d10, [x4, " FP_R10_OFF "]\n\t"
"ldr d11, [x4, " FP_R11_OFF "]\n\t"
"ldr d12, [x4, " FP_R12_OFF "]\n\t"
"ldr d13, [x4, " FP_R13_OFF "]\n\t"
"ldr d14, [x4, " FP_R14_OFF "]\n\t"
"ldr d15, [x4, " FP_R15_OFF "]\n\t"
"ldr x5, [x5, " SC_SP_OFF "]\n\t"
"mov sp, x5\n\t"
"ret\n"
:
: [x0] "m"(uc->uc_mcontext.regs[0]),
[x1] "m"(uc->uc_mcontext.regs[1]),
[x2] "m"(uc->uc_mcontext.regs[2]),
[x3] "m"(uc->uc_mcontext.regs[3]),
[x19] "m"(uc->uc_mcontext.regs[19]),
[x20] "m"(uc->uc_mcontext.regs[20]),
[x21] "m"(uc->uc_mcontext.regs[21]),
[x22] "m"(uc->uc_mcontext.regs[22]),
[x23] "m"(uc->uc_mcontext.regs[23]),
[x24] "m"(uc->uc_mcontext.regs[24]),
[x25] "m"(uc->uc_mcontext.regs[25]),
[x26] "m"(uc->uc_mcontext.regs[26]),
[x27] "m"(uc->uc_mcontext.regs[27]),
[x28] "m"(uc->uc_mcontext.regs[28]),
[x29] "m"(uc->uc_mcontext.regs[29]), /* FP */
[x30] "m"(uc->uc_mcontext.regs[30]), /* LR */
[d8] "m"(GET_FPCTX(uc)->vregs[8]),
[d9] "m"(GET_FPCTX(uc)->vregs[9]),
[d10] "m"(GET_FPCTX(uc)->vregs[10]),
[d11] "m"(GET_FPCTX(uc)->vregs[11]),
[d12] "m"(GET_FPCTX(uc)->vregs[12]),
[d13] "m"(GET_FPCTX(uc)->vregs[13]),
[d14] "m"(GET_FPCTX(uc)->vregs[14]),
[d15] "m"(GET_FPCTX(uc)->vregs[15]),
[sp] "m"(uc->uc_mcontext.sp)
: "x0", "x1", "x2", "x3", "x19", "x20", "x21", "x22", "x23", "x24",
"x25", "x26", "x27", "x28", "x29", "x30"
);
:
: [uc_mcontext] "r"(uc_mcontext),
[fpctx] "r"(fpctx)
);
}
else
{
Expand Down