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LibC: Make scanf always copy its va_list

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On x86_64 GCC implements va_list as an array. This makes the syntax
for taking a pointer to it break & crash. The workaround / solution is
to create a copy. Since va_list is a tiny struct referencing the
actual varargs, this is little overhead (especially compared to
va_args itself)
This commit is contained in:
Peter Bindels 2021-07-16 22:01:35 +02:00 • committed by Gunnar Beutner
parent 3cca9e6704
commit 85c2ad94d5
1 changed files with 5 additions and 1 deletions
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6
Userland/Libraries/LibC/scanf.cpp
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@ -383,6 +383,9 @@ extern "C" int vsscanf(const char* input, const char* format, va_list ap)
int elements_matched = 0;
va_list copy;
__builtin_va_copy(copy, ap);
while (!format_lexer.is_eof()) {
format_lexer.ignore_while(isspace);
if (!format_lexer.next_is('%')) {
@ -537,7 +540,7 @@ extern "C" int vsscanf(const char* input, const char* format, va_list ap)
}
}
auto* ap_or_null = !suppress_assignment ? (va_list*)&ap : nullptr;
auto* ap_or_null = !suppress_assignment ? (va_list*)&copy : nullptr;
// Now try to read.
switch (conversion_specifier) {
@ -616,6 +619,7 @@ extern "C" int vsscanf(const char* input, const char* format, va_list ap)
}
}
}
va_end(copy);
return elements_matched;
}