From: Mathieu Desnoyers Date: Tue, 19 Apr 2011 01:21:31 +0000 (-0400) Subject: Markers: make __ust_marker_ptrs PIC X-Git-Tag: v1.9.1~393 X-Git-Url: http://git.lttng.org./?a=commitdiff_plain;h=7b2cd9b7a2ac58f4765809b180b417674154dbfc;p=lttng-ust.git Markers: make __ust_marker_ptrs PIC > As I prepared the 0.12 release for Debian, I noticed that libust.so was > not PIC: > > $ readelf -d libust/.libs/libust.so.0.0.0 | grep TEXTREL > 0x0000000000000016 (TEXTREL) 0x0 > > Since all of the objects in libust are built with -fPIC, I thought > perhaps there was some assembly added between 0.11 and 0.12 that > contained text relocations. I bisected the two tags down to the > offending commit: > > eb5d20c68aaf73661ffc02ba8fea3683c0358702 > > Within that commit, it seems to be a problem in include/ust/marker.h > with these lines: > > @@ -129,7 +124,12 @@ struct marker { > [...] > + /*".section __markers_ptrs\n\t"*/ \ > + ".section __markers_ptrs,\"a\",@progbits\n\t" \ > > If I make the __markers_ptrs section writable, with: > > ".section __markers_ptrs,\"aw\"\n\t > > TEXTREL goes away and everything seems okay, tests pass. Is this > a correct solution? I don't understand why the section must be writable > to avoid relocations, can anyone explain? Oh.. I think I see. __markers_ptrs contains pointers to another section that must be populated by the dynamic linker (thus at runtime). If the section is read-only, the linker cannot update them at load time, so a relocation table is probably needed. Reported-by: Jon Bernard Signed-off-by: Mathieu Desnoyers --- diff --git a/include/ust/marker.h b/include/ust/marker.h index 48504179..1a3d74e9 100644 --- a/include/ust/marker.h +++ b/include/ust/marker.h @@ -124,7 +124,7 @@ struct ust_marker { _ASM_PTR "(1f)\n\t" /* location */ \ ".previous\n\t" \ /*".section __ust_marker_ptrs\n\t"*/ \ - ".section __ust_marker_ptrs,\"a\"\n\t" \ + ".section __ust_marker_ptrs,\"aw\"\n\t" \ _ASM_PTR "(2b)\n\t" \ ".previous\n\t" \ "1:\n\t" \