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[libc] Independent strcat/strncat/stpcpy #142643

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Merged
merged 3 commits into from
Jun 12, 2025
Merged

[libc] Independent strcat/strncat/stpcpy #142643

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843f9c4
[libc] Independent strcat/strncat
michaelrj-google Jun 3, 2025
5233127
fix stpcpy as well
michaelrj-google Jun 4, 2025
9543b52
use builtin instead of inline memcpy
michaelrj-google Jun 5, 2025
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3 changes: 0 additions & 3 deletions libc/src/string/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -87,7 +87,6 @@ add_entrypoint_object(
HDRS
stpcpy.h
DEPENDS
.mempcpy
.string_utils
)

Expand All @@ -108,7 +107,6 @@ add_entrypoint_object(
HDRS
strcat.h
DEPENDS
.strcpy
.string_utils
libc.include.llvm-libc-types.size_t
)
Expand Down Expand Up @@ -265,7 +263,6 @@ add_entrypoint_object(
HDRS
strncat.h
DEPENDS
.strncpy
.string_utils
libc.include.llvm-libc-types.size_t
)
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5 changes: 2 additions & 3 deletions libc/src/string/stpcpy.cpp
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Expand Up @@ -8,7 +8,6 @@

#include "src/string/stpcpy.h"
#include "src/__support/macros/config.h"
#include "src/string/mempcpy.h"
#include "src/string/string_utils.h"

#include "src/__support/common.h"
Expand All @@ -18,8 +17,8 @@ namespace LIBC_NAMESPACE_DECL {
LLVM_LIBC_FUNCTION(char *, stpcpy,
(char *__restrict dest, const char *__restrict src)) {
size_t size = internal::string_length(src) + 1;
char *result =
reinterpret_cast<char *>(LIBC_NAMESPACE::mempcpy(dest, src, size));
__builtin_memcpy(dest, src, size);
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We have a definition for this in libc/src/string/memory_utils/generic/builtin.h.

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is there a reason to call that version instead of calling the builtin directly?

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Mostly was wondering if there would be an easier way to select which flavor of memcpy we wanted. Might've been better as a template function than this macro dispatch but that's a big change.

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I'd be interested in making memcpy specialization template controlled, though to keep the includes for different architectures separate we would probably still need some amount of macro control. I think that's probably a topic for a separate PR though.

char *result = dest + size;

if (result != nullptr)
return result - 1;
Expand Down
9 changes: 5 additions & 4 deletions libc/src/string/strcat.cpp
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Expand Up @@ -9,7 +9,6 @@
#include "src/string/strcat.h"
#include "src/__support/macros/config.h"
#include "src/__support/macros/null_check.h"
#include "src/string/strcpy.h"
#include "src/string/string_utils.h"

#include "src/__support/common.h"
Expand All @@ -21,9 +20,11 @@ LLVM_LIBC_FUNCTION(char *, strcat,
LIBC_CRASH_ON_NULLPTR(dest);
LIBC_CRASH_ON_NULLPTR(src);
size_t dest_length = internal::string_length(dest);
size_t src_length = internal::string_length(src);
LIBC_NAMESPACE::strcpy(dest + dest_length, src);
dest[dest_length + src_length] = '\0';
size_t i;
for (i = 0; src[i] != '\0'; ++i)
dest[dest_length + i] = src[i];

dest[dest_length + i] = '\0';
return dest;
}

Expand Down
10 changes: 5 additions & 5 deletions libc/src/string/strncat.cpp
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Expand Up @@ -10,7 +10,6 @@
#include "src/__support/macros/config.h"
#include "src/__support/macros/null_check.h"
#include "src/string/string_utils.h"
#include "src/string/strncpy.h"

#include "src/__support/common.h"

Expand All @@ -23,11 +22,12 @@ LLVM_LIBC_FUNCTION(char *, strncat,
LIBC_CRASH_ON_NULLPTR(dest);
LIBC_CRASH_ON_NULLPTR(src);
}
size_t src_length = internal::string_length(src);
size_t copy_amount = src_length > count ? count : src_length;
size_t dest_length = internal::string_length(dest);
LIBC_NAMESPACE::strncpy(dest + dest_length, src, copy_amount);
dest[dest_length + copy_amount] = '\0';
size_t i;
for (i = 0; i < count && src[i] != '\0'; ++i)
dest[dest_length + i] = src[i];

dest[dest_length + i] = '\0';
return dest;
}

Expand Down
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