591a12a1d4
This patch handles another aspect of the ELFv2 ABI, which unfortunately requires common code changes. In ELFv2, functions may provide both a global and a local entry point. The global entry point (where the function symbol points to) is intended to be used for function-pointer or cross-module (PLT) calls, and requires r12 to be set up to the entry point address itself. The local entry point (which is found at a fixed offset after the global entry point, as defined by bits in the symbol table entries' st_other field), instead expects r2 to be set up to the current TOC. Now, when setting a breakpoint on a function by name, you really want that breakpoint to trigger either way, no matter whether the function is called via its local or global entry point. Since the global entry point will always fall through into the local entry point, the way to achieve that is to simply set the breakpoint at the local entry point. One way to do that would be to have prologue parsing skip the code sequence that makes up the global entry point. Unfortunately, this does not work reliably, since -for optimized code- GDB these days will not actuall invoke the prologue parsing code but instead just set the breakpoint at the symbol address and rely on DWARF being correct at any point throughout the function ... Unfortunately, I don't really see any way to express the notion of local entry points with the current set of gdbarch callbacks. Thus this patch adds a new callback, skip_entrypoint, that is somewhat analogous to skip_prologue, but is called every time GDB needs to determine a function start address, even in those cases where GDB decides to not call skip_prologue. As a side effect, the skip_entrypoint implementation on ppc64 does not need to perform any instruction parsing; it can simply rely on the local entry point flags in the symbol table entry. With this implemented, two test cases would still fail to set the breakpoint correctly, but that's because they use the construct: gdb_test "break *hello" Now, using "*hello" explicitly instructs GDB to set the breakpoint at the numerical value of "hello" treated as function pointer, so it will by definition only hit the global entry point. I think this behaviour is unavoidable, but acceptable -- most people do not use this construct, and if they do, they get what they asked for ... In one of those two test cases, use of this construct is really not appropriate. I think this was added way back when as a means to work around prologue skipping problems on some platforms. These days that shouldn't really be necessary any more ... For the other (step-bt), we really want to make sure backtracing works on the very first instruction of the routine. To enable that test also on powerpc64le-linux, we can modify the code to call the test function via function pointer (which makes it use the global entry point in the ELFv2 ABI). gdb/ChangeLog: * gdbarch.sh (skip_entrypoint): New callback. * gdbarch.c, gdbarch.h: Regenerate. * symtab.c (skip_prologue_sal): Call gdbarch_skip_entrypoint. * infrun.c (fill_in_stop_func): Likewise. * ppc-linux-tdep.c: Include "elf/ppc64.h". (ppc_elfv2_elf_make_msymbol_special): New function. (ppc_elfv2_skip_entrypoint): Likewise. (ppc_linux_init_abi): Install them for ELFv2. gdb/testsuite/ChangeLog: * gdb.base/sigbpt.exp: Do not use "*" when setting breakpoint on a function. * gdb.base/step-bt.c: Call hello via function pointer to make sure its first instruction is executed on powerpc64le-linux.
41 lines
1.3 KiB
C
41 lines
1.3 KiB
C
/* This testcase is part of GDB, the GNU debugger.
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Copyright 2006-2014 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#include <stdio.h>
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void
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hello (void)
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{
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printf ("Hello world.\n");
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}
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/* The test case uses "break *hello" to make sure to step at the very
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first instruction of the function. This causes a problem running
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the test on powerpc64le-linux, since the first instruction belongs
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to the global entry point prologue, which is skipped when doing a
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local direct function call. To make sure that first instruction is
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indeed being executed and the breakpoint hits, we make sure to call
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the routine via an indirect call. */
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void (*ptr) (void) = hello;
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int
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main (void)
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{
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ptr ();
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return 0;
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}
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