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Message-Id: <20230104150719.252185-1-gabravier@gmail.com>
Date: Wed, 4 Jan 2023 16:07:19 +0100
From: Gabriel Ravier <gabravier@...il.com>
To: musl@...ts.openwall.com
Cc: Gabriel Ravier <gabravier@...il.com>
Subject: [PATCH] fix return value of wcs{,n}cmp for near-limits signed wchar_t values
The standard states that:
> Unless explicitly stated otherwise, the functions described in
this subclause order two wide characters the same way as two
integers of the underlying integer type designated by `wchar_t`.
> [...]
> The `wcscmp` function returns an integer greater than, equal to,
or less than zero, accordingly as the wide string pointed to by s1
is greater than, equal to, or less than the wide string pointed to
by s2.
> The `wcsncmp` function returns an integer greater than, equal to,
or less than zero, accordingly as the possibly null-terminated
array pointed to by s1 is greater than, equal to, or less than the
possibly null-terminated array pointed to by s2
- N3047 (latest C draft as of the time of writing)
Yet a simple test program such as this:
#include <wchar.h>
#include <stdio.h>
int main()
{
wchar_t str1[2] = { WCHAR_MAX, L'\0' };
wchar_t str2[2] = { WCHAR_MIN, L'\0' };
printf("%d\n", wcscmp(str1, str2));
printf("%d\n", wcsncmp(str1, str2, 1));
}
Will fail to run correctly according to this specification on musl (on
targets that have signed wchar_t), as it will print -1 instead of
1 (it should print 1, since WCHAR_MAX > WCHAR_MIN).
This appears to be due to the fact that musl uses a simple subtraction
to implement wcscmp and wcsncmp, which may result in an overflow.
This patch fixes this by replacing the subtraction with a little bit
of code that orders the characters correctly, returning -1 if the
character from the first string is smaller than the one from the
second, 0 if they are equal and 1 if the character from the first
string is larger than the one from the second
---
src/string/wcscmp.c | 2 +-
src/string/wcsncmp.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/src/string/wcscmp.c b/src/string/wcscmp.c
index 26eeee70..286ec3ea 100644
--- a/src/string/wcscmp.c
+++ b/src/string/wcscmp.c
@@ -3,5 +3,5 @@
int wcscmp(const wchar_t *l, const wchar_t *r)
{
for (; *l==*r && *l && *r; l++, r++);
- return *l - *r;
+ return *l < *r ? -1 : *l > *r;
}
diff --git a/src/string/wcsncmp.c b/src/string/wcsncmp.c
index 4ab32a92..2b3558bf 100644
--- a/src/string/wcsncmp.c
+++ b/src/string/wcsncmp.c
@@ -3,5 +3,5 @@
int wcsncmp(const wchar_t *l, const wchar_t *r, size_t n)
{
for (; n && *l==*r && *l && *r; n--, l++, r++);
- return n ? *l - *r : 0;
+ return n ? (*l < *r ? -1 : *l > *r) : 0;
}
--
2.38.1
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