Android Q
The libc source as below:
__attribute__((constructor(1))) static void __libc_preinit() {
// The linker has initialized its copy of the global stack_chk_guard, and
filled in the main
// thread's TLS slot with that value. Initialize the local global stack guard
with its value.
__stack_chk_guard =
reinterpret_cast<uintptr_t>(__get_tls()[TLS_SLOT_STACK_GUARD]);
__libc_preinit_impl();
}
__attribute__((noinline))
static void __libc_preinit_impl() {
// Register libc.so's copy of the TLS generation variable so the linker can
// update it when it loads or unloads a shared object.
TlsModules& tls_modules = __libc_shared_globals()->tls_modules;
tls_modules.generation_libc_so = &__libc_tls_generation_copy;
__libc_tls_generation_copy = tls_modules.generation;
__libc_init_globals();
__libc_init_common();
// Hooks for various libraries to let them know that we're starting up.
TestInitImpl();
}
static void TestInitImpl() {
printf("%s enter\n", __func__);
void * handle = dlopen("liblog.so", RTLD_NOW ); -----------This is
most important call, If call dlopen success, and then malloc trace is not
available now; If Not success, the malloc trace is okay;
printf("handle:%p\n", handle);
}
The test main as below:
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
int main(int argc, char ** argv) {
char * p = (char *)malloc(2048);
p[2049] = 5;
printf("p=%p p[2049]=%d malloc=%p \n", p, p[2049], malloc);
(void) argc;
(void) argv;
return 0;
}
The valgrind output as below:
localhost:/system/bin # ./valgrind --undef-value-errors=no --trace-malloc=yes
./test64
MallocInitImpl enter
handle:0xcf2625b55fe1209
==7131== Memcheck, a memory error detector
==7131== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==7131== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==7131== Command: ./test64
==7131==
linker: Warning: "/system_Q_EA3/lib64/valgrind/vgpreload_core-arm64-linux.so"
has unsupported flags DT_FLAGS_1=0x421 (ignoring unsupported flags)
WARNING: linker: Warning:
"/system_Q_EA3/lib64/valgrind/vgpreload_core-arm64-linux.so" has unsupported
flags DT_FLAGS_1=0x421 (ignoring unsupported flags)
linker: Warning:
"/system_Q_EA3/lib64/valgrind/vgpreload_memcheck-arm64-linux.so" has
unsupported flags DT_FLAGS_1=0x421 (ignoring unsupported flags)
WARNING: linker: Warning:
"/system_Q_EA3/lib64/valgrind/vgpreload_memcheck-arm64-linux.so" has
unsupported flags DT_FLAGS_1=0x421 (ignoring unsupported flags)
--7131-- malloc(48) = 0x60AA040
--7131-- malloc(1024) = 0x60AA0B0-----------------------------before call
dlopen in libc module , these text show me malloc trace is okay.
MallocInitImpl enter
--7131-- free(0x0)
handle:0x25bc73725878d53 -----------------------after print these text (it
mean dlopen success in libc) , malloc trace is failure;
p=0x6813000 p[2049]=5 malloc=0x5d0f32c----------------------these text mean
main alloc some memory ;
==7131==
==7131== HEAP SUMMARY:
==7131== in use at exit: 1,072 bytes in 2 blocks
==7131== total heap usage: 2 allocs, 0 frees, 1,072 bytes allocated
==7131==
==7131== LEAK SUMMARY:
==7131== definitely lost: 0 bytes in 0 blocks
==7131== indirectly lost: 0 bytes in 0 blocks
==7131== possibly lost: 0 bytes in 0 blocks
==7131== still reachable: 1,072 bytes in 2 blocks
==7131== suppressed: 0 bytes in 0 blocks
==7131== Rerun with --leak-check=full to see details of leaked memory
==7131==
==7131== For counts of detected and suppressed errors, rerun with: -v
==7131== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
-----邮件原件-----
发件人: John Reiser [mailto:jrei...@bitwagon.com]
发送时间: 2019年4月23日 23:19
收件人: valgrind-users@lists.sourceforge.net
主题: Re: [Valgrind-users] Some question about linker dlopen with valgrind
>> On the Android OS, there is a question about the linker program
>> with vaglrind memcheck.
Which version of Android?
>>
>> The 1^st experiment, the libc module *do*call the dlopen
>> function to load some shared object, before the linker call the
>> pre_init functions ( before transfer the cpu control to the main ),
>> and then the valgrind *can not*trace malloc leak;
>>
>> The second experiment, the libc module *do not*call the
>> dlopen function to load some shared object, before the linker call
>> the pre_init functions ( before transfer the cpu control to the main
>> ), and then the valgrind *can* trace malloc leak;
>>
>> I want to know why , and how to make valgrind can trace memory
>> leak, while the libc module call the dlopen function to load some so,
>> before the linker call the pre-init functions.
According to
https://docs.oracle.com/cd/E19683-01/816-1386/6m7qcobks/index.html
the order of execution is:
1. linker resolves and fetches all DT_NEEDED modules (shared libraries),
and performs all relocations for the entire process image
2. linker calls DT_PREINIT_ARRAY functions of the main program, in order
(only a main program may have DT_PREINIT_ARRAY; a shared library MUST NOT)
3. in dependency order (topological bottom-up) of all loaded modules (main
program
and shared libraries): linker calls DT_INIT and then DT_INIT_ARRAY (in
order)
for the module
4. linker transfers control to the ElfXX_Ehdr.e_entry address of the main
program
It is undefined what happens if a DT_PREINIT_ARRAY, DT_INIT_ARRAY, or DT_INIT
function calls dlopen, particularly if the newly-loaded module depends on any
other modules, whether or not those modules have been loaded already. (The
dependent module might not be initialized yet.)
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