[PATCH] The local variables "sym" and "bestsym" in dladdr function are assigned initial values to NULL

["liucheng (G)" <liucheng32@huawei.com>]

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Dear all,



The code bellow in the dladdr function has different behaviors at different optimization levels.

2219         if (bestsym && besterr > bestsym->st_size-1) {

2220                 best = 0;

2221                 bestsym = 0;

2222         }



Case of O1(arm32 little-endian):

154:         e3580000        cmp   r8, #0

158:         0a000003        beq   16c <dladdr+0x16c>

15c:         e5983008        ldr    r3, [r8, #8]

160:         e2433001        sub   r3, r3, #1

164:         e153000a        cmp   r3, sl

168:         3a000011        bcc   1bc <dladdr+0x1b4>



Case of O2:

75e00:       e5942044        ldr     r2, [r4, #68]   ; 0x44

75e04:       e2433001        sub     r3, r3, #1

75e08:       e5941004        ldr     r1, [r4, #4]

75e0c:       e1530009        cmp     r3, r9

75e10:       2a000007        bcs     75e34 <dladdr+0xfc>

75e14:       e8870006        stm     r7, {r1, r2}



In case of O2, the first part "bestsym" has been optimized, which may cause segment fault.



[patch]

Signed-off-by: l00383200 <liucheng32@huawei.com<mailto:liucheng32@huawei.com>>

---

ldso/dynlink.c | 3 ++-

1 file changed, 2 insertions(+), 1 deletion(-)



diff --git a/ldso/dynlink.c b/ldso/dynlink.c

index 7cb66db..c5f5fb7 100644

--- a/ldso/dynlink.c

+++ b/ldso/dynlink.c

@@ -2175,7 +2175,8 @@ int dladdr(const void *addr_arg, Dl_info *info)

{

       size_t addr = (size_t)addr_arg;

       struct dso *p;

-        Sym *sym, *bestsym;

+       Sym *sym = NULL;

+       Sym *bestsym = NULL;

       uint32_t nsym;

       char *strings;

       size_t best = 0;

--

1.8.5.6





[testcase]

------------

#define _GNU_SOURCE

#include <link.h>

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#include <dlfcn.h>



static int callback(struct dl_phdr_info *info, size_t size, void *data)

{

        int j,ret;

        printf ("name=%s (%d segments)\n", info->dlpi_name, info->dlpi_phnum);



        if(!strcmp(info->dlpi_name,"/lib/ld-musl-arm.so.1")) {

                printf("ld-musl-arm have no indo\n");

                return 0;

        }



        for (j = 0; j < info->dlpi_phnum; j++) {

                void* addr = (void *) (info->dlpi_addr + info->dlpi_phdr[j].p_vaddr);

                printf ("\t\t header %2d: address=%10p\n", j, addr);

                Dl_info dlinfo;

                ret = dladdr(addr, &dlinfo);



                printf("\t\t\t %s : %s.", dlinfo.dli_fname, dlinfo.dli_sname);



                if((addr == NULL && ret == 0) || (addr != NULL && ret == 1)) {

                        printf(" dladdr pass return:%d\n",ret);

                } else {

                        printf(" dladdr error return:%d\n",ret);

                }

        }



        return 0;



}



int main (int argc, char *argv[])

{

        dl_iterate_phdr(callback, NULL);

        exit(EXIT_SUCCESS);

}

------------


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