#8935: Obscure linker bug leads to crash in GHCi
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Reporter: simonmar | Owner: simonmar
Type: bug | Status: patch
Priority: high | Milestone: 7.8.3
Component: Runtime System | Version: 7.8.1-rc2
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture: Unknown/Multiple
Type of failure: GHCi crash | Difficulty: Rocket Science
Test Case: | Blocked By:
Blocking: | Related Tickets:
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Comment (by simonmar):
No, no, it does not look bad at all. The address looks strange but that
is caused by the fact that it was created by the dynamic linker. Look at
*defl_env and *env in the second program in comment:25. The addresses
match and I checked they really point to the environment array!
Well, every time we call `dlsym` passing the handle of a `dlopen`'d
library, we get a bogus result. This happens for both `libgmp` and
`libpthread` (after modifying the `libpthread` path to point to the real
.so, not the linker script).
{{{
#include
#include
#include
char *so = "/usr/lib/x86_64-linux-gnu/libgmp.so";
char *so2 = "/lib/x86_64-linux-gnu/libpthread.so.0";
extern char**environ;
int main(int argc, char *argv[])
{
void *deflt, *hdl;
char ***env;
deflt = dlopen(NULL, RTLD_LAZY | RTLD_GLOBAL);
printf("&environ = %p, environ = %p\n", &environ, environ);
env = dlsym(deflt,"environ");
printf("dlsym(deflt, \"environ\") = %p, *env = %p\n", env, *env );
hdl = dlopen(so, RTLD_LAZY);
if (hdl == NULL) {
printf("%s\n", dlerror());
exit(1);
}
env = dlsym(hdl,"environ");
printf("dlsym(\"libgmp\", \"environ\") = %p, *env = %p\n", env, *env);
hdl = dlopen(so2, RTLD_LAZY);
if (hdl == NULL) {
printf("%s\n", dlerror());
exit(1);
}
env = dlsym(hdl,"environ");
printf("dlsym(\"libpthread\", \"environ\") = %p, *env = %p\n", env,
*env);
}
}}}
output:
{{{
$ ./a.out
&environ = 0x601078, environ = 0x7fffc44c2008
dlsym(deflt, "environ") = 0x601078, *env = 0x7fffc44c2008
dlsym("libgmp", "environ") = 0x2ba8772b64e8, *env = (nil)
dlsym("libpthread", "environ") = 0x2ba8772b64e8, *env = (nil)
}}}
--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8935#comment:33
GHC http://www.haskell.org/ghc/
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