142 lines
5.6 KiB
Diff
142 lines
5.6 KiB
Diff
http://sourceware.org/ml/gdb-patches/2011-02/msg00630.html
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Subject: [patch] [i386] Fix {,un}prelinked libraries for attach/core-load
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Hi,
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please see comments in the patch. The adjusted testcase FAILs on i386.
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"Prelink", March 4, 2004 - by Jakub Jelinek:
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http://people.redhat.com/jakub/prelink.pdf
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primarily section 7 - REL to RELA conversion
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An example of unprelinked -> prelinked library change:
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Program Headers:
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Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
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- LOAD 0x000000 0x00000000 0x00000000 0x00538 0x00538 R E 0x1000
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- LOAD 0x000538 0x00001538 0x00001538 0x00100 0x00110 RW 0x1000
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- DYNAMIC 0x000550 0x00001550 0x00001550 0x000c8 0x000c8 RW 0x4
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- NOTE 0x0000f4 0x000000f4 0x000000f4 0x00024 0x00024 R 0x4
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- GNU_EH_FRAME 0x0004e8 0x000004e8 0x000004e8 0x00014 0x00014 R 0x4
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+ LOAD 0x000000 0x411b3000 0x411b3000 0x00558 0x00558 R E 0x1000
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+ LOAD 0x000558 0x411b4558 0x411b4558 0x00100 0x00110 RW 0x1000
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+ DYNAMIC 0x000570 0x411b4570 0x411b4570 0x000c8 0x000c8 RW 0x4
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+ NOTE 0x0000f4 0x411b30f4 0x411b30f4 0x00024 0x00024 R 0x4
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+ GNU_EH_FRAME 0x000508 0x411b3508 0x411b3508 0x00014 0x00014 R 0x4
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GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0x4
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So far GDB expected all such displacements will be always PAGE_SIZE aligned.
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This applies for example for re-prelinking of an already prelinked file.
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But it does not apply for prelinking of an unprelinked file or unprelinking of
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a prelinked file, there can be arbitrary displacement.
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It affects i386 (=i686, prelink doc reports also ARM and MIPS) which uses REL.
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x86_64 always uses RELA, therefore I have not noticed it so far. i386 still
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has to be supported.
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This affects both attachment to a PID and core file loads.
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This applies in real world if you transfer a core file between hosts and try to
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backtrace them, libraries of both hosts may differ whether they are / are not
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prelinked.
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I could implement some (displacement-forgiving and prelink-modifications
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forgiving) comparison of both DYNAMIC segments found. But I do not think it is
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useful, if the DYNAMIC address from linkmap vs. bfd do not match it is still a
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better chance to try a displacement to make them match. Keeping the file
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relocation cannot work anyway when the DYNAMIC address is verified as wrong.
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No regressions on {x86_64,x86_64-m32,i686}-fedora15-linux-gnu.
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Mostly do you agree the DYNAMIC content does not have to be verifed?
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Do you have any comments on the in-code long comments?
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Thanks,
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Jan
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gdb/
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2011-02-22 Jan Kratochvil <jan.kratochvil@redhat.com>
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Fix libraries displacement if they change whether they were prelinked.
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* solib-svr4.c (LM_ADDR_CHECK): Set L_ADDR even if the DYNAMIC pointer
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does not match. Comment why.
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gdb/testsuite/
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2011-02-22 Jan Kratochvil <jan.kratochvil@redhat.com>
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* gdb.base/break-interp-lib.c (v, vptr): New variables.
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* gdb.base/break-interp.exp (test_attach): New comment.
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--- a/gdb/solib-svr4.c
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+++ b/gdb/solib-svr4.c
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@@ -237,11 +237,11 @@ LM_ADDR_CHECK (struct so_list *so, bfd *abfd)
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Even on PPC it must be zero-aligned at least for MINPAGESIZE. */
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+ l_addr = l_dynaddr - dynaddr;
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+
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if ((l_addr & (minpagesize - 1)) == 0
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&& (l_addr & align) == ((l_dynaddr - dynaddr) & align))
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{
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- l_addr = l_dynaddr - dynaddr;
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-
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if (info_verbose)
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printf_unfiltered (_("Using PIC (Position Independent Code) "
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"prelink displacement %s for \"%s\".\n"),
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@@ -249,9 +249,20 @@ LM_ADDR_CHECK (struct so_list *so, bfd *abfd)
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so->so_name);
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}
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else
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- warning (_(".dynamic section for \"%s\" "
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- "is not at the expected address "
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- "(wrong library or version mismatch?)"), so->so_name);
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+ {
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+ /* There is no way to verify the library file matches. prelink
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+ can during prelinking of an unprelinked file (or unprelinking
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+ of a prelinked file) shift the DYNAMIC segment by arbitrary
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+ offset without any page size alignment. There is no way to
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+ find out the ELF header and/or Program Headers for a limited
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+ verification if it they match. One could do a verification
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+ of the DYNAMIC segment. Still the found address is the best
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+ one GDB could find. */
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+
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+ warning (_(".dynamic section for \"%s\" "
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+ "is not at the expected address "
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+ "(wrong library or version mismatch?)"), so->so_name);
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+ }
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}
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set_addr:
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--- a/gdb/testsuite/gdb.base/break-interp-lib.c
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+++ b/gdb/testsuite/gdb.base/break-interp-lib.c
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@@ -20,6 +20,10 @@
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#include <assert.h>
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#include <stdio.h>
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+/* Force REL->RELA conversion on i386, see "Prelink", March 4, 2004. */
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+volatile int v[2];
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+volatile int *vptr = &v[1];
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+
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void
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libfunc (const char *action)
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{
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--- a/gdb/testsuite/gdb.base/break-interp.exp
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+++ b/gdb/testsuite/gdb.base/break-interp.exp
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@@ -352,6 +352,14 @@ proc test_attach {file displacement {relink_args ""}} {
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# test simplicity, we merged this test and the test above by not
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# restoring $INTERP after $EXEC prelink. $INTERP gets restored
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# later below.
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+ #
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+ # `(wrong library or version mismatch?)' messages are printed for
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+ # $binfile_lib on platforms converting REL->RELA relocations by
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+ # prelink (such as on i386). There is no reliable way to verify
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+ # the library file matches the running library in such case but
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+ # GDB at least attempts to set the right displacement. We test
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+ # `libfunc' is present in the backtrace and therefore the
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+ # displacement has been guessed right.
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if [prelink$relink $relink_args [file tail $exec]] {
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# /proc/PID/exe cannot be loaded as it is "EXECNAME (deleted)".
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