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author | Ulrich Weigand <ulrich.weigand@de.ibm.com> | 2014-02-04 18:44:14 +0100 |
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committer | Ulrich Weigand <ulrich.weigand@de.ibm.com> | 2014-02-04 18:44:14 +0100 |
commit | 591a12a1d4c8843343eb999145d8bcc1efedf408 (patch) | |
tree | 3ee9bd92c9be0f9d47afdc936fc4f1995f21920a /gdb/gdbarch.h | |
parent | cc0e89c519912e0e4e75a2fc0d836f715cdc6806 (diff) | |
download | gdb-591a12a1d4c8843343eb999145d8bcc1efedf408.zip gdb-591a12a1d4c8843343eb999145d8bcc1efedf408.tar.gz gdb-591a12a1d4c8843343eb999145d8bcc1efedf408.tar.bz2 |
PowerPC64 ELFv2 ABI: skip global entry point code
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.
Diffstat (limited to 'gdb/gdbarch.h')
-rw-r--r-- | gdb/gdbarch.h | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h index b28a80e..9698e11 100644 --- a/gdb/gdbarch.h +++ b/gdb/gdbarch.h @@ -486,6 +486,24 @@ typedef CORE_ADDR (gdbarch_skip_main_prologue_ftype) (struct gdbarch *gdbarch, C extern CORE_ADDR gdbarch_skip_main_prologue (struct gdbarch *gdbarch, CORE_ADDR ip); extern void set_gdbarch_skip_main_prologue (struct gdbarch *gdbarch, gdbarch_skip_main_prologue_ftype *skip_main_prologue); +/* On some platforms, a single function may provide multiple entry points, + e.g. one that is used for function-pointer calls and a different one + that is used for direct function calls. + In order to ensure that breakpoints set on the function will trigger + no matter via which entry point the function is entered, a platform + may provide the skip_entrypoint callback. It is called with IP set + to the main entry point of a function (as determined by the symbol table), + and should return the address of the innermost entry point, where the + actual breakpoint needs to be set. Note that skip_entrypoint is used + by GDB common code even when debugging optimized code, where skip_prologue + is not used. */ + +extern int gdbarch_skip_entrypoint_p (struct gdbarch *gdbarch); + +typedef CORE_ADDR (gdbarch_skip_entrypoint_ftype) (struct gdbarch *gdbarch, CORE_ADDR ip); +extern CORE_ADDR gdbarch_skip_entrypoint (struct gdbarch *gdbarch, CORE_ADDR ip); +extern void set_gdbarch_skip_entrypoint (struct gdbarch *gdbarch, gdbarch_skip_entrypoint_ftype *skip_entrypoint); + typedef int (gdbarch_inner_than_ftype) (CORE_ADDR lhs, CORE_ADDR rhs); extern int gdbarch_inner_than (struct gdbarch *gdbarch, CORE_ADDR lhs, CORE_ADDR rhs); extern void set_gdbarch_inner_than (struct gdbarch *gdbarch, gdbarch_inner_than_ftype *inner_than); |