我写了这个简单的小测试应用程序，但valgrind报告我正在失去记忆。
你可以直接复制并粘贴它并使用valgrind运行它。也许那些经验丰富的c程序员可以立即看到内存泄漏，但我不能。我将发布一次运行的输出。如果我在vert_layout_new的for循环中注释掉大部分代码，那么大多数错误就会消失。
为什么我会泄漏这么多内存并造成无效读取？
valgrind --leak-check=full -v /opt/./main
==12908== Memcheck, a memory error detector
==12908== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==12908== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==12908== Command: /opt/./main
==12908==
--12908-- Valgrind options:
--12908-- --leak-check=full
--12908-- -v
--12908-- Contents of /proc/version:
--12908-- Linux version 4.2.0-0.bpo.1-amd64 (debian-kernel@lists.debian.org) (gcc version 4.9.2 (Debian 4.9.2-10) ) #1 SMP Debian 4.2.6-3~bpo8+2 (2015-12-14)
--12908--
--12908-- Arch and hwcaps: AMD64, LittleEndian, amd64-cx16-lzcnt-rdtscp-sse3-avx-avx2-bmi
--12908-- Page sizes: currently 4096, max supported 4096
--12908-- Valgrind library directory: /opt/valgrind/lib/valgrind
--12908-- Reading syms from /opt/main
--12908-- Reading syms from /lib/x86_64-linux-gnu/ld-2.19.so
--12908-- Considering /lib/x86_64-linux-gnu/ld-2.19.so ..
--12908-- .. CRC mismatch (computed 65ef7209 wanted 26b223d2)
--12908-- Considering /usr/lib/debug/lib/x86_64-linux-gnu/ld-2.19.so ..
--12908-- .. CRC is valid
--12908-- Reading syms from /opt/valgrind/lib/valgrind/memcheck-amd64-linux
--12908-- object doesn't have a dynamic symbol table
--12908-- Scheduler: using generic scheduler lock implementation.
--12908-- Reading suppressions file: /opt/valgrind/lib/valgrind/default.supp
==12908== embedded gdbserver: reading from /tmp/vgdb-pipe-from-vgdb-to-12908-by-blubee-on-???
==12908== embedded gdbserver: writing to /tmp/vgdb-pipe-to-vgdb-from-12908-by-blubee-on-???
==12908== embedded gdbserver: shared mem /tmp/vgdb-pipe-shared-mem-vgdb-12908-by-blubee-on-???
==12908==
==12908== TO CONTROL THIS PROCESS USING vgdb (which you probably
==12908== don't want to do, unless you know exactly what you're doing,
==12908== or are doing some strange experiment):
==12908== /opt/valgrind/lib/valgrind/../../bin/vgdb --pid=12908 ...command...
==12908==
==12908== TO DEBUG THIS PROCESS USING GDB: start GDB like this
==12908== /path/to/gdb /opt/./main
==12908== and then give GDB the following command
==12908== target remote | /opt/valgrind/lib/valgrind/../../bin/vgdb --pid=12908
==12908== --pid is optional if only one valgrind process is running
==12908==
--12908-- REDIR: 0x4017950 (ld-linux-x86-64.so.2:strlen) redirected to 0x3809ea41 (vgPlain_amd64_linux_REDIR_FOR_strlen)
--12908-- Reading syms from /opt/valgrind/lib/valgrind/vgpreload_core-amd64-linux.so
--12908-- Reading syms from /opt/valgrind/lib/valgrind/vgpreload_memcheck-amd64-linux.so
==12908== WARNING: new redirection conflicts with existing -- ignoring it
--12908-- old: 0x04017950 (strlen ) R-> (0000.0) 0x3809ea41 vgPlain_amd64_linux_REDIR_FOR_strlen
--12908-- new: 0x04017950 (strlen ) R-> (2007.0) 0x04c2ac80 strlen
--12908-- REDIR: 0x4017700 (ld-linux-x86-64.so.2:index) redirected to 0x4c2a830 (index)
--12908-- REDIR: 0x4017920 (ld-linux-x86-64.so.2:strcmp) redirected to 0x4c2bd30 (strcmp)
--12908-- REDIR: 0x4018650 (ld-linux-x86-64.so.2:mempcpy) redirected to 0x4c2ee30 (mempcpy)
--12908-- Reading syms from /lib/x86_64-linux-gnu/libc-2.19.so
--12908-- Considering /lib/x86_64-linux-gnu/libc-2.19.so ..
--12908-- .. CRC mismatch (computed e5556398 wanted 5318f0bf)
--12908-- Considering /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.19.so ..
--12908-- .. CRC is valid
--12908-- REDIR: 0x4eb8e10 (libc.so.6:strcasecmp) redirected to 0x4a236fe (_vgnU_ifunc_wrapper)
--12908-- REDIR: 0x4ebb100 (libc.so.6:strncasecmp) redirected to 0x4a236fe (_vgnU_ifunc_wrapper)
--12908-- REDIR: 0x4eb85e0 (libc.so.6:memcpy@GLIBC_2.2.5) redirected to 0x4a236fe (_vgnU_ifunc_wrapper)
--12908-- REDIR: 0x4eb6960 (libc.so.6:rindex) redirected to 0x4c2a510 (rindex)
--12908-- REDIR: 0x4ebf7a0 (libc.so.6:strchrnul) redirected to 0x4c2e960 (strchrnul)
--12908-- REDIR: 0x4eb87c0 (libc.so.6:__GI_mempcpy) redirected to 0x4c2eb60 (__GI_mempcpy)
argc:/opt/./main
--12908-- REDIR: 0x4eaf980 (libc.so.6:calloc) redirected to 0x4c298f0 (calloc)
--12908-- REDIR: 0x4eb4c60 (libc.so.6:strlen) redirected to 0x4c2abc0 (strlen)
Position
Color
TexCoord 0
==12908== Invalid read of size 8
==12908== at 0x4006D5: vert_layout_new (in /opt/main)
==12908== by 0x400817: main (in /opt/main)
==12908== Address 0x51dc0e8 is 0 bytes after a block of size 24 alloc'd
==12908== at 0x4C29986: calloc (vg_replace_malloc.c:711)
==12908== by 0x4005F3: vert_attrib_new (in /opt/main)
==12908== by 0x400791: main (in /opt/main)
==12908==
==12908== Invalid read of size 8
==12908== at 0x4006DB: vert_layout_new (in /opt/main)
==12908== by 0x400817: main (in /opt/main)
==12908== Address 0x51dc0f0 is 8 bytes after a block of size 24 alloc'd
==12908== at 0x4C29986: calloc (vg_replace_malloc.c:711)
==12908== by 0x4005F3: vert_attrib_new (in /opt/main)
==12908== by 0x400791: main (in /opt/main)
==12908==
==12908== Invalid read of size 8
==12908== at 0x4006E3: vert_layout_new (in /opt/main)
==12908== by 0x400817: main (in /opt/main)
==12908== Address 0x51dc0f8 is 16 bytes after a block of size 24 alloc'd
==12908== at 0x4C29986: calloc (vg_replace_malloc.c:711)
==12908== by 0x4005F3: vert_attrib_new (in /opt/main)
==12908== by 0x400791: main (in /opt/main)
==12908==
==12908== Invalid read of size 8
==12908== at 0x40070E: vert_layout_new (in /opt/main)
==12908== by 0x400817: main (in /opt/main)
==12908== Address 0x51dc0f8 is 16 bytes after a block of size 24 alloc'd
==12908== at 0x4C29986: calloc (vg_replace_malloc.c:711)
==12908== by 0x4005F3: vert_attrib_new (in /opt/main)
==12908== by 0x400791: main (in /opt/main)
==12908==
--12908-- REDIR: 0x4eaf650 (libc.so.6:free) redirected to 0x4c28ca2 (free)
==12908==
==12908== HEAP SUMMARY:
==12908== in use at exit: 72 bytes in 3 blocks
==12908== total heap usage: 6 allocs, 3 frees, 264 bytes allocated
==12908==
==12908== Searching for pointers to 3 not-freed blocks
==12908== Checked 66,184 bytes
==12908==
==12908== 24 bytes in 1 blocks are definitely lost in loss record 1 of 3
==12908== at 0x4C29986: calloc (vg_replace_malloc.c:711)
==12908== by 0x4005F3: vert_attrib_new (in /opt/main)
==12908== by 0x400791: main (in /opt/main)
==12908==
==12908== 24 bytes in 1 blocks are definitely lost in loss record 2 of 3
==12908== at 0x4C29986: calloc (vg_replace_malloc.c:711)
==12908== by 0x4005F3: vert_attrib_new (in /opt/main)
==12908== by 0x4007B2: main (in /opt/main)
==12908==
==12908== 24 bytes in 1 blocks are definitely lost in loss record 3 of 3
==12908== at 0x4C29986: calloc (vg_replace_malloc.c:711)
==12908== by 0x4005F3: vert_attrib_new (in /opt/main)
==12908== by 0x4007CC: main (in /opt/main)
==12908==
==12908== LEAK SUMMARY:
==12908== definitely lost: 72 bytes in 3 blocks
==12908== indirectly lost: 0 bytes in 0 blocks
==12908== possibly lost: 0 bytes in 0 blocks
==12908== still reachable: 0 bytes in 0 blocks
==12908== suppressed: 0 bytes in 0 blocks
==12908==
==12908== ERROR SUMMARY: 15 errors from 7 contexts (suppressed: 0 from 0)
==12908==
==12908== 3 errors in context 1 of 7:
==12908== Invalid read of size 8
==12908== at 0x40070E: vert_layout_new (in /opt/main)
==12908== by 0x400817: main (in /opt/main)
==12908== Address 0x51dc0f8 is 16 bytes after a block of size 24 alloc'd
==12908== at 0x4C29986: calloc (vg_replace_malloc.c:711)
==12908== by 0x4005F3: vert_attrib_new (in /opt/main)
==12908== by 0x400791: main (in /opt/main)
==12908==
==12908==
==12908== 3 errors in context 2 of 7:
==12908== Invalid read of size 8
==12908== at 0x4006E3: vert_layout_new (in /opt/main)
==12908== by 0x400817: main (in /opt/main)
==12908== Address 0x51dc0f8 is 16 bytes after a block of size 24 alloc'd
==12908== at 0x4C29986: calloc (vg_replace_malloc.c:711)
==12908== by 0x4005F3: vert_attrib_new (in /opt/main)
==12908== by 0x400791: main (in /opt/main)
==12908==
==12908==
==12908== 3 errors in context 3 of 7:
==12908== Invalid read of size 8
==12908== at 0x4006DB: vert_layout_new (in /opt/main)
==12908== by 0x400817: main (in /opt/main)
==12908== Address 0x51dc0f0 is 8 bytes after a block of size 24 alloc'd
==12908== at 0x4C29986: calloc (vg_replace_malloc.c:711)
==12908== by 0x4005F3: vert_attrib_new (in /opt/main)
==12908== by 0x400791: main (in /opt/main)
==12908==
==12908==
==12908== 3 errors in context 4 of 7:
==12908== Invalid read of size 8
==12908== at 0x4006D5: vert_layout_new (in /opt/main)
==12908== by 0x400817: main (in /opt/main)
==12908== Address 0x51dc0e8 is 0 bytes after a block of size 24 alloc'd
==12908== at 0x4C29986: calloc (vg_replace_malloc.c:711)
==12908== by 0x4005F3: vert_attrib_new (in /opt/main)
==12908== by 0x400791: main (in /opt/main)
==12908==
==12908== ERROR SUMMARY: 15 errors from 7 contexts (suppressed: 0 from 0)
这是运行该程序的输出。
{{1}}
答案 0 :(得分：1)
此处发生无效读取（请参阅内联注释）：
vert_layout* vert_layout_new(vert_attrib* attributes, size_t count) {
vert_layout* out = calloc(1, sizeof(vert_layout));
out->attributes = calloc(1, sizeof(vert_attrib) * count);
for (size_t i = 0; i < count; i++) {
// attributes is a pointer to a single vert_attribute,
// not an array
out->attributes[i] = attributes[i];
out->vert_size += attributes[i].attrib_size;
}
return out;
}
int main(int argc, char* argv[]) {
...
vert_attrib** attribs = calloc(1, sizeof(vert_attrib) * 3);
...
// passing in attribs[0], which points to vert_attrib
// also passing in size 4 instead of 3
vert_layout* l = vert_layout_new(*attribs, 4);
...
}
您应该将attribs传递给vert_layout_new而不是*attribs，并相应地更改定义。
至于内存泄漏，您可以释放attribs，但不释放单独分配的各个数组元素。
修复：
vert_layout* vert_layout_new(vert_attrib** attributes, size_t count) {
vert_layout* out = calloc(1, sizeof(vert_layout));
out->attributes = calloc(1, sizeof(vert_attrib) * count);
for (size_t i = 0; i < count; i++) {
out->attributes[i] = *(attributes[i]);
out->vert_size += attributes[i]->attrib_size;
}
return out;
}
int main(int argc, char* argv[]) {
....
vert_layout* l = vert_layout_new(attribs, 3);
....
for (size_t i = 0; i < 3; i++) {
free(attribs[i]);
}
free(attribs);
...
}
答案 1 :(得分：0)
当你释放'l-＆gt;属性'时，你正在泄漏数组插槽0,1和2中的指针。
答案 2 :(得分：0)
vert_layout_new(*attribs, 4);导致未定义的行为。 *attribs（aka。attribs[0]）是指向单个属性的指针。但是vert_layout_new函数会尝试从该内存位置读取4个属性。
换句话说，在main中，您分配了3个单独的分配，每个分配包含1个属性，但在vert_layout_new中，您只读取在同一分配中相邻的属性。
无效读取来自您尝试在attribs[0]指向的分配结束后再读取3个属性。
另外，正如Les指出的那样，你从未释放vert_attrib_new分配的内存。
要解决此问题，您需要在两个位置使用相同的策略：在main中连续分配属性（这意味着更改vert_attrib_new函数），或者使vert_layout_new接受{ {1}}（这也需要vert_attrib **包含vert_layout，除非你想在那时复制属性。）
它可能会帮助您在纸上绘制您想要的内存布局的图表，箭头显示指向的位置。