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trans/codegen_c: Collapse Rust asm! double-dollar escape for GCC inline asm #412

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trans/codegen_c: Collapse Rust asm! double-dollar escape for GCC inline asm #412

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26 changes: 24 additions & 2 deletions src/trans/codegen_c.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5618,11 +5618,33 @@ namespace {
if( (Target_GetCurSpec().m_arch.m_name == "x86" || Target_GetCurSpec().m_arch.m_name == "x86_64") && !se.options.att_syntax )
m_of << ".intel_syntax noprefix; ";
bool escape_percent = true || !inputs.empty() || !outputs.empty();
// Rust's `asm!` templates are passed verbatim to LLVM, where `$$`
// is the escape for a literal `$` (LLVM IR uses `$N` for operand
// references). The GCC inline-asm backend has no such escape, and
// a stray `$` survives into the GAS input as e.g. `int $0x80` —
// which GAS rejects in `.intel_syntax noprefix` mode with
// "operand type mismatch". Collapse `$$` here: drop it entirely
// for Intel-syntax blocks (so `int $$0x80` -> `int 0x80`), and
// halve it for AT&T blocks (so the immediate prefix survives).
auto xlat_dollars = [&](const std::string& s) {
std::string r;
r.reserve(s.size());
for(size_t i = 0; i < s.size(); ++i) {
if(s[i] == '$' && i+1 < s.size() && s[i+1] == '$') {
if(se.options.att_syntax) r += '$';
i++;
}
else {
r += s[i];
}
}
return r;
};
Comment on lines +5621 to +5642

@thepowersgang thepowersgang May 24, 2026

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This translation should be in operator<<(::std::ostream& os, const FmtGccAsm& x) instead of as pre-processing pass.

for(const auto& l : se.lines)
{
for(const auto& f : l.frags)
{
m_of << FmtGccAsm(f.before, escape_percent);
m_of << FmtGccAsm(xlat_dollars(f.before), escape_percent);
MIR_ASSERT(mir_res, arg_mappings.at(f.index) != UINT_MAX, stmt);
m_of << "%";
if( arg_mappings.at(f.index) == UINT8_MAX-1 ) {
Expand All @@ -5644,7 +5666,7 @@ namespace {
}
m_of << arg_mappings.at(f.index);
}
m_of << FmtGccAsm(l.trailing, escape_percent);
m_of << FmtGccAsm(xlat_dollars(l.trailing), escape_percent);
m_of << ";\\n ";
}
if( (Target_GetCurSpec().m_arch.m_name == "x86" || Target_GetCurSpec().m_arch.m_name == "x86_64") && !se.options.att_syntax )
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