MDEV-34266 removed a #pragma that would silence a GCC warning about possible missing NUL terminator when invoking strncpy(). It looks like the warning depends on some optimization settings.
Initially I thought that the warning got smarter in GCC 14, which was recently made the default compiler in Debian Sid, but I found examples of the warnings in the build logs also with GCC 12.2.0.
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is caused by
MDEV-34266safe_strcpy() includes an unnecessary conditional branch
This would result in another type of warning elsewhere, which I guess would also be output by some older versions of GCC:
10.6 2e580dc2a8da4aaf3a7f1b3cfb4f897dbb5f7089 with patch
In file included from /mariadb/10.6/include/my_bitmap.h:22,
from /mariadb/10.6/sql/log_event.h:36,
from /mariadb/10.6/sql/rpl_parallel.h:4,
from /mariadb/10.6/sql/rpl_parallel.cc:2:
/mariadb/10.6/include/m_string.h: In function ‘int rpt_handle_event(rpl_parallel_thread::queued_event*, rpl_parallel_thread*)’:
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
261 | strncpy(dst, src, dst_size);
| ^
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
/mariadb/10.6/include/m_string.h: In member function ‘rpl_parallel_thread::queued_event* rpl_parallel_thread::get_qev(Log_event*, ulonglong, Relay_log_info*)’:
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
/mariadb/10.6/include/m_string.h: In member function ‘rpl_parallel_thread::queued_event* rpl_parallel_thread::retry_get_qev(Log_event*, queued_event*, const char*, ulonglong, ulonglong)’:
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
/mariadb/10.6/include/m_string.h: In function ‘void* handle_rpl_parallel_thread(void*)’:
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
The 511 would likely be FN_REFLEN-1.
It looks like the #pragma must be reinstated to keep GCC 14 happy.
Marko Mäkelä
added a comment - Here is an example of a warning from GCC 14.2.0:
10.6 2e580dc2a8da4aaf3a7f1b3cfb4f897dbb5f7089
In file included from /mariadb/10.6/sql/sql_plugin.h:33,
from /mariadb/10.6/sql/mysqld.h:22,
from /mariadb/10.6/sql/semisync.h:21,
from /mariadb/10.6/sql/semisync_master.h:22,
from /mariadb/10.6/sql/semisync_master.cc:20:
/mariadb/10.6/include/m_string.h: In member function ‘int Repl_semi_sync_master::report_binlog_update(THD*, THD*, const char*, my_off_t)’:
/mariadb/10.6/include/m_string.h:260:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ specified bound 512 equals destination size [-Wstringop-truncation]
260 | strncpy(dst, src, dst_size);
| ^
I tried to fix it with the following patch:
diff --git a/include/m_string.h b/include/m_string.h
index 0cd6ff4513e..f9b8656623d 100644
--- a/include/m_string.h
+++ b/include/m_string.h
@@ -249,6 +249,7 @@ static inline void lex_string_set3(LEX_CSTRING *lex_str, const char *c_str,
static inline void safe_strcpy(char *dst, size_t dst_size, const char *src)
{
DBUG_ASSERT(dst_size > 0);
+ dst_size--;
/* 1) IF there is a 0 byte in the first dst_size bytes of src, strncpy will
* 0-terminate dst, and pad dst with additional 0 bytes out to dst_size.
@@ -258,7 +259,7 @@ static inline void safe_strcpy(char *dst, size_t dst_size, const char *src)
*/
strncpy(dst, src, dst_size);
- dst[dst_size - 1]= 0;
+ dst[dst_size]= 0;
}
/**
This would result in another type of warning elsewhere, which I guess would also be output by some older versions of GCC:
10.6 2e580dc2a8da4aaf3a7f1b3cfb4f897dbb5f7089 with patch
In file included from /mariadb/10.6/include/my_bitmap.h:22,
from /mariadb/10.6/sql/log_event.h:36,
from /mariadb/10.6/sql/rpl_parallel.h:4,
from /mariadb/10.6/sql/rpl_parallel.cc:2:
/mariadb/10.6/include/m_string.h: In function ‘int rpt_handle_event(rpl_parallel_thread::queued_event*, rpl_parallel_thread*)’:
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
261 | strncpy(dst, src, dst_size);
| ^
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
/mariadb/10.6/include/m_string.h: In member function ‘rpl_parallel_thread::queued_event* rpl_parallel_thread::get_qev(Log_event*, ulonglong, Relay_log_info*)’:
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
/mariadb/10.6/include/m_string.h: In member function ‘rpl_parallel_thread::queued_event* rpl_parallel_thread::retry_get_qev(Log_event*, queued_event*, const char*, ulonglong, ulonglong)’:
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
/mariadb/10.6/include/m_string.h: In function ‘void* handle_rpl_parallel_thread(void*)’:
/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]
The 511 would likely be FN_REFLEN-1 .
It looks like the #pragma must be reinstated to keep GCC 14 happy.
MDEV-34266 removed a {{#pragma}} that would silence a GCC warning about possible missing NUL terminator when invoking {{strncpy()}}. It looks like the check got smarter in GCC 14, which was recently made the default compiler in Debian Sid.
MDEV-34266 removed a {{#pragma}} that would silence a GCC warning about possible missing NUL terminator when invoking {{strncpy()}}. It looks like the warning depends on some optimization settings.
Initially I thought that the warning got smarter in GCC 14, which was recently made the default compiler in Debian Sid, but I found examples of the warnings in the build logs also with GCC 12.2.0.
Bug
Critical
Here is an example of a warning from GCC 14.2.0:
10.6 2e580dc2a8da4aaf3a7f1b3cfb4f897dbb5f7089
In file included from /mariadb/10.6/sql/sql_plugin.h:33,from /mariadb/10.6/sql/mysqld.h:22,from /mariadb/10.6/sql/semisync.h:21,from /mariadb/10.6/sql/semisync_master.h:22,from /mariadb/10.6/sql/semisync_master.cc:20:/mariadb/10.6/include/m_string.h: In member function ‘int Repl_semi_sync_master::report_binlog_update(THD*, THD*, const char*, my_off_t)’:/mariadb/10.6/include/m_string.h:260:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ specified bound 512 equals destination size [-Wstringop-truncation]260 | strncpy(dst, src, dst_size);| ^I tried to fix it with the following patch:
diff --git a/include/m_string.h b/include/m_string.hindex 0cd6ff4513e..f9b8656623d 100644--- a/include/m_string.h+++ b/include/m_string.h@@ -249,6 +249,7 @@ static inline void lex_string_set3(LEX_CSTRING *lex_str, const char *c_str,static inline void safe_strcpy(char *dst, size_t dst_size, const char *src){DBUG_ASSERT(dst_size > 0);+ dst_size--;/* 1) IF there is a 0 byte in the first dst_size bytes of src, strncpy will* 0-terminate dst, and pad dst with additional 0 bytes out to dst_size.@@ -258,7 +259,7 @@ static inline void safe_strcpy(char *dst, size_t dst_size, const char *src)*/strncpy(dst, src, dst_size);- dst[dst_size - 1]= 0;+ dst[dst_size]= 0;}This would result in another type of warning elsewhere, which I guess would also be output by some older versions of GCC:
10.6 2e580dc2a8da4aaf3a7f1b3cfb4f897dbb5f7089 with patch
In file included from /mariadb/10.6/include/my_bitmap.h:22,from /mariadb/10.6/sql/log_event.h:36,from /mariadb/10.6/sql/rpl_parallel.h:4,from /mariadb/10.6/sql/rpl_parallel.cc:2:/mariadb/10.6/include/m_string.h: In function ‘int rpt_handle_event(rpl_parallel_thread::queued_event*, rpl_parallel_thread*)’:/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]261 | strncpy(dst, src, dst_size);| ^/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]/mariadb/10.6/include/m_string.h: In member function ‘rpl_parallel_thread::queued_event* rpl_parallel_thread::get_qev(Log_event*, ulonglong, Relay_log_info*)’:/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]/mariadb/10.6/include/m_string.h: In member function ‘rpl_parallel_thread::queued_event* rpl_parallel_thread::retry_get_qev(Log_event*, queued_event*, const char*, ulonglong, ulonglong)’:/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]/mariadb/10.6/include/m_string.h: In function ‘void* handle_rpl_parallel_thread(void*)’:/mariadb/10.6/include/m_string.h:261:10: warning: ‘char* __builtin_strncpy(char*, const char*, long unsigned int)’ output may be truncated copying 511 bytes from a string of length 511 [-Wstringop-truncation]The 511 would likely be FN_REFLEN-1.
It looks like the #pragma must be reinstated to keep GCC 14 happy.