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[Backport][main to 0.9] | fix(thread): complete context-switch clobbers and reserve Win64 shadow space (#1720) #1725

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Merged
Coldwings merged 2 commits into from
Nov 4, 2026
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[Backport][main to 0.9] | fix(thread): complete context-switch clobbers and reserve Win64 shadow space (#1720) #1725

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66f2cd4
fix(thread): complete context-switch clobbers and reserve Win64 shado…
Coldwings Nov 2, 2026
a14f89f
fix(thread): resolve Win64 thread stub conflict for release/0.9
Coldwings Nov 2, 2026
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65 changes: 56 additions & 9 deletions thread/thread.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -761,6 +761,53 @@ namespace photon
static_assert(offsetof(thread, start) == 0x48, "...");
#pragma GCC diagnostic pop

// switch_context() and switch_context_defer() hide a function call inside
// an asm statement, so the compiler can not see what happens across it:
// other photon threads run in between, and they may change any register
// and any memory. So, besides the GPRs, the asm statements must declare
// as clobbered all the vector / mask / flag registers that are not
// preserved by the switch, as well as "memory". Otherwise the compiler
// may keep a value in e.g. %xmm0 across the switch, and get garbage back.
//
// Note that the ABI's caller-saved (volatile) registers, e.g. all xmm on
// x86-64 SysV, are NOT implied clobbered here, as the compiler does not
// treat an asm statement as a call. Nor does the C++ call of these inline
// functions help: once inlined, there is no call boundary at all; and
// even if not, -fipa-ra (enabled at -O2) lets the caller keep values in
// the volatile registers that the callee, as told by these very clobber
// lists, does not use. On the other hand, the callee-saved ones (xmm6-15
// on Win64, v8-v15 on aarch64) must be listed too, as the switch does not
// save them like a real callee would do.
//
// See the GCC manual, Extended Asm, "Clobbers and Scratch Registers", and
// Optimize Options, "-fipa-ra".
#if defined(__x86_64__)
#ifdef __AVX512F__
#define VECTOR_CLOBBERS_AVX512 \
"xmm16", "xmm17", "xmm18", "xmm19", "xmm20", "xmm21", "xmm22", "xmm23", \
"xmm24", "xmm25", "xmm26", "xmm27", "xmm28", "xmm29", "xmm30", "xmm31", \
"k0", "k1", "k2", "k3", "k4", "k5", "k6", "k7",
#else
#define VECTOR_CLOBBERS_AVX512
#endif
#define VECTOR_CLOBBERS VECTOR_CLOBBERS_AVX512 \
"xmm0", "xmm1", "xmm2", "xmm3", "xmm4", "xmm5", "xmm6", "xmm7", \
"xmm8", "xmm9", "xmm10", "xmm11", "xmm12", "xmm13", "xmm14", "xmm15"
#elif defined(__aarch64__) || defined(__arm64__)
#ifdef __ARM_FEATURE_SVE
#define VECTOR_CLOBBERS_SVE \
"p0", "p1", "p2", "p3", "p4", "p5", "p6", "p7", \
"p8", "p9", "p10", "p11", "p12", "p13", "p14", "p15",
#else
#define VECTOR_CLOBBERS_SVE
#endif
#define VECTOR_CLOBBERS VECTOR_CLOBBERS_SVE \
"v0", "v1", "v2", "v3", "v4", "v5", "v6", "v7", \
"v8", "v9", "v10", "v11", "v12", "v13", "v14", "v15", \
"v16", "v17", "v18", "v19", "v20", "v21", "v22", "v23", \
"v24", "v25", "v26", "v27", "v28", "v29", "v30", "v31"
#endif

#if defined(__x86_64__)
#if !defined(_WIN64)
asm(
Expand Down Expand Up @@ -808,7 +855,7 @@ R"(
: "+r"(t), "+r"(f)
: // "0"(t), "1"(f)
: "rax", "rbx", "rcx", "rdx", "r8", "r9", "r10", "r11",
"r12", "r13", "r14", "r15");
"r12", "r13", "r14", "r15", VECTOR_CLOBBERS, "memory");
}

inline void switch_context_defer(thread* from, thread* to,
Expand All @@ -825,7 +872,7 @@ R"(
: "+r"(t), "+r"(f), "+r"(a), "+r"(d)
: // "0"(t), "1"(f), "2"(a), "3"(d)
: "rax", "rbx", "r8", "r9", "r10", "r11", "r12", "r13", "r14",
"r15");
"r15", VECTOR_CLOBBERS, "memory");
}
#else // _WIN64
asm(
Expand All @@ -851,9 +898,11 @@ R"(
jmp *%rdx
)"

// Reserve 32 bytes of shadow space for the calls to
// the thread entry and _photon_thread_die.
DEF_ASM_FUNC(_photon_thread_stub)
R"(
call _asan_start
sub $32, %rsp
mov 0x40(%rbp), %rcx
movq $0, 0x40(%rbp)
call *0x48(%rbp)
Expand All @@ -874,8 +923,7 @@ R"(
: // "0"(t), "1"(f)
: "rax", "rbx", "rsi", "rdi", "r8", "r9",
"r10", "r11", "r12", "r13", "r14", "r15",
"xmm6", "xmm7", "xmm8", "xmm9", "xmm10",
"xmm11", "xmm12", "xmm13", "xmm14", "xmm15");
VECTOR_CLOBBERS, "memory");
}

inline void switch_context_defer(thread* from, thread* to,
Expand All @@ -893,8 +941,7 @@ R"(
: // "0"(t), "1"(f), "2"(a), "3"(d)
: "rax", "rbx", "rsi", "rdi", "r10",
"r11", "r12", "r13", "r14", "r15",
"xmm6", "xmm7", "xmm8", "xmm9", "xmm10",
"xmm11", "xmm12", "xmm13", "xmm14", "xmm15");
VECTOR_CLOBBERS, "memory");
}
#endif // _WIN64

Expand Down Expand Up @@ -960,7 +1007,7 @@ R"(
"x2", "x3", "x4", "x5", "x6", "x7", "x8",
// Corouptable register, may change ,should save
"x9", "x10", "x11", "x12", "x13", "x14", "x15", "x16",
"x17", "x18");
"x17", "x18", VECTOR_CLOBBERS, "cc", "memory");
}

inline void switch_context_defer(thread* from, thread* to,
Expand All @@ -978,7 +1025,7 @@ R"(
: "x19", "x20", "x21", "x22", "x23", "x24", "x25", "x26",
"x27", "x28", "x29", "x30", "x4", "x5", "x6", "x7", "x8",
"x9", "x10", "x11", "x12", "x13", "x14", "x15", "x16",
"x17", "x18");
"x17", "x18", VECTOR_CLOBBERS, "cc", "memory");
}
#ifdef __clang__
#pragma GCC diagnostic pop
Expand Down
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