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WIP Make stacktraces across compartments more robust #672

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8 changes: 8 additions & 0 deletions CMakeLists.txt
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Original file line number Diff line number Diff line change
@@ -1,6 +1,14 @@
cmake_minimum_required(VERSION 4.0)
project(IA2Phase2)

# Ensure all project-built executables and shared libraries emit DWARF call
# frame information for unwinding through generated call gates and DSOs.
add_compile_options(
"-funwind-tables"
"-fasynchronous-unwind-tables"
)
add_link_options("-Wl,--eh-frame-hdr")

# Feature flags
option(IA2_DEBUG "Enable debug telemetry and runtime checks" OFF)

Expand Down
53 changes: 52 additions & 1 deletion tools/rewriter/GenCallAsm.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -219,6 +219,32 @@ static void add_comment_line(AsmWriter &aw, const std::string &s) {
aw.ss << std::endl;
}

static void add_cfi_line(AsmWriter &aw, const std::string &s) {
add_asm_line(aw, ".cfi_" + s);
}

static void emit_x86_target_stack_frame_setup(AsmWriter &aw) {
add_comment_line(
aw,
"Build a synthetic frame on the target stack so GDB can unwind across the stack switch");
add_asm_line(aw, "subq $16, %rsp");
add_asm_line(aw, "movq %r14, (%rsp)");
add_asm_line(aw, "movq %r15, 8(%rsp)");
add_asm_line(aw, "movq %rsp, %rbp");
add_cfi_line(aw, "def_cfa %rbp, 16");
add_cfi_line(aw, "offset %rbp, -16");
}

static void emit_x86_target_stack_frame_teardown(AsmWriter &aw) {
add_comment_line(
aw,
"Tear down the synthetic target-stack frame before restoring the caller stack");
add_asm_line(aw, "movq (%rbp), %rbp");
add_asm_line(aw, "addq $16, %rsp");
add_cfi_line(aw, "def_cfa %rbp, 16");
add_cfi_line(aw, "offset %rbp, -16");
}

static void emit_reg_push(AsmWriter &aw, const ArgLocation &loc) {
assert(!loc.is_stack());
if (loc.is_128bit_float()) {
Expand Down Expand Up @@ -464,12 +490,18 @@ static void emit_prologue(AsmWriter &aw, uint32_t caller_pkey, uint32_t target_p
if (arch == Arch::X86) {
// Save the old frame pointer and set the frame pointer for the call gate
add_asm_line(aw, "pushq %rbp");
add_cfi_line(aw, "def_cfa_offset 16");
add_cfi_line(aw, "offset %rbp, -16");
add_asm_line(aw, "movq %rsp, %rbp");
add_cfi_line(aw, "def_cfa_register %rbp");
// Save registers that are preserved across function calls before switching to
// the other compartment's stack. This is on the caller's stack so it's not in
// the diagram above.
for (auto &r : x86_preserved_registers) {
for (size_t i = 0; i < x86_preserved_registers.size(); i++) {
auto &r = x86_preserved_registers[i];
add_asm_line(aw, "pushq %"s + r);
int cfi_offset = -24 - 8 * static_cast<int>(i);
add_cfi_line(aw, "offset %"s + r + ", " + std::to_string(cfi_offset));
}
} else if (arch == Arch::Aarch64) {
// Frame pointer and link register need to be saved first, to make backtraces work
Expand Down Expand Up @@ -962,9 +994,12 @@ static void emit_epilogue(AsmWriter &aw, uint32_t caller_pkey, Arch arch) {
for (auto r = x86_preserved_registers.rbegin(); r != x86_preserved_registers.rend();
r++) {
add_asm_line(aw, "popq %"s + *r);
add_cfi_line(aw, "restore %"s + *r);
}
// Restore the caller's frame pointer
add_asm_line(aw, "popq %rbp");
add_cfi_line(aw, "def_cfa %rsp, 8");
add_cfi_line(aw, "restore %rbp");
} else if (arch == Arch::Aarch64) {
// Restore callee-saved registers
for (int i = 0; i < aarch64_preserved_registers.size(); ++i) {
Expand Down Expand Up @@ -1215,6 +1250,7 @@ std::string emit_asm_wrapper(
// Set the symbol type
add_asm_line(aw, ".type "s + wrapper_name + ", @function");
add_asm_line(aw, wrapper_name + ":");
add_cfi_line(aw, "startproc");

emit_prologue(aw, caller_pkey, target_pkey, arch);

Expand Down Expand Up @@ -1266,7 +1302,15 @@ std::string emit_asm_wrapper(
x86_emit_intermediate_pkru(aw, caller_pkey, target_pkey, "rcx", "rdx");
}

if (arch == Arch::X86) {
add_comment_line(aw, "Save the caller frame chain before switching to the target stack");
add_asm_line(aw, "movq %rbp, %r14");
add_asm_line(aw, "movq 8(%rbp), %r15");
}
emit_switch_stacks(aw, caller_pkey, target_pkey, arch);
if (arch == Arch::X86) {
emit_x86_target_stack_frame_setup(aw);
}

emit_copy_args(aw, args, wrapper_args, stack_return_size, stack_return_padding, indirect_arg_size, indirect_arg_padding, stack_alignment, stack_arg_size, stack_arg_padding, wrapper_stack_arg_size, caller_pkey, arch);

Expand All @@ -1283,8 +1327,14 @@ std::string emit_asm_wrapper(
emit_free_stack_space(aw, stack_arg_size + stack_arg_padding + stack_alignment, arch);

emit_copy_stack_returns(aw, stack_return_size, stack_return_padding, stack_arg_size, stack_arg_padding, caller_pkey, target_pkey, arch);
if (arch == Arch::X86) {
emit_x86_target_stack_frame_teardown(aw);
}

emit_switch_stacks(aw, target_pkey, caller_pkey, arch);
if (arch == Arch::X86) {
add_cfi_line(aw, "def_cfa %rbp, 16");
}

emit_scrub_regs(aw, target_pkey, rets, false, arch);

Expand All @@ -1308,6 +1358,7 @@ std::string emit_asm_wrapper(
emit_epilogue(aw, caller_pkey, arch);

emit_return(aw);
add_cfi_line(aw, "endproc");

// Set the symbol size
add_asm_line(aw, ".size "s + wrapper_name + ", .-" + wrapper_name);
Expand Down
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