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Re: [PATCH] [SPARC64] Figure out where a longjmp will land
- From: jose dot marchesi at oracle dot com (Jose E. Marchesi)
- To: Tom Tromey <tromey at redhat dot com>
- Cc: gdb-patches at sourceware dot org
- Date: Tue, 08 Oct 2013 23:53:09 +0200
- Subject: Re: [PATCH] [SPARC64] Figure out where a longjmp will land
- Authentication-results: sourceware.org; auth=none
- References: <87y563k71b dot fsf at oracle dot com> <87d2nffr53 dot fsf at fleche dot redhat dot com>
Jose> Note that in sparc64 glibc does not install probes in setjmp, nor it
Jose> mangles pointers.
In this case adding the probes is marginal; but you will probably want
to write the probe support for sparc64 in gdb anyway, because there are
other probes available that provide more noticeable benefits...
Yes, I will take a look at the several places where probes are used in
other architetures.
Jose> + return X_A(insn);
Space before the "(".
Updated patch follows.
Many thanks for reviewing :)
2013-10-08 Jose E. Marchesi <jose.marchesi@oracle.com>
* sparc-tdep.c (sparc_is_annulled_branch_insn): New function.
* sparc-tdep.h: And its prototype.
* sparc64-linux-tdep.c (sparc64_linux_get_longjmp_target): New
function.
(sparc64_linux_init_abi): Register the get_longjmp_target hook.
Index: sparc-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/sparc-tdep.c,v
retrieving revision 1.233
diff -u -r1.233 sparc-tdep.c
--- sparc-tdep.c 24 Jun 2013 22:18:32 -0000 1.233
+++ sparc-tdep.c 8 Oct 2013 17:13:35 -0000
@@ -121,6 +121,17 @@
return ((insn & 0xc1c00000) == 0);
}
+/* Return non-zero if the instruction corresponding to PC is an
+ "annulled" branch, i.e. the annul bit is set. */
+
+int
+sparc_is_annulled_branch_insn (CORE_ADDR pc)
+{
+ const unsigned long insn = sparc_fetch_instruction (pc);
+
+ return X_A (insn);
+}
+
/* OpenBSD/sparc includes StackGhost, which according to the author's
website http://stackghost.cerias.purdue.edu "... transparently and
automatically protects applications' stack frames; more
Index: sparc-tdep.h
===================================================================
RCS file: /cvs/src/src/gdb/sparc-tdep.h,v
retrieving revision 1.33
diff -u -r1.33 sparc-tdep.h
--- sparc-tdep.h 1 Jan 2013 06:32:51 -0000 1.33
+++ sparc-tdep.h 8 Oct 2013 17:13:35 -0000
@@ -202,6 +202,12 @@
extern void sparc_collect_rwindow (const struct regcache *regcache,
CORE_ADDR sp, int regnum);
+
+
+extern int sparc_is_annulled_branch_insn (CORE_ADDR pc);
+
+
+
/* Register offsets for SunOS 4. */
extern const struct sparc_gregset sparc32_sunos4_gregset;
extern const struct sparc_fpregset sparc32_sunos4_fpregset;
Index: sparc64-linux-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/sparc64-linux-tdep.c,v
retrieving revision 1.31
diff -u -r1.31 sparc64-linux-tdep.c
--- sparc64-linux-tdep.c 1 Jan 2013 06:32:51 -0000 1.31
+++ sparc64-linux-tdep.c 8 Oct 2013 17:13:35 -0000
@@ -233,6 +233,54 @@
}
+/* Figure out where a longjmp will land. Get the args out of the
+ output registers. We expect the first arg to be a pointer to the
+ jmp_buf structure from which we extract the address that we will
+ land at. This address is copied into PC. This routine returns
+ non-zero on success. */
+
+static int
+sparc64_linux_get_longjmp_target (struct frame_info *frame, CORE_ADDR *pc)
+{
+ struct gdbarch *gdbarch = get_frame_arch (frame);
+ struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
+ CORE_ADDR jb_addr;
+ gdb_byte buf[8];
+
+ jb_addr = get_frame_register_unsigned (frame, SPARC_O0_REGNUM);
+
+ /* setjmp and longjmp in SPARC64 are implemented in glibc using the
+ setcontext and getcontext system calls respectively. These
+ system calls operate on ucontext_t structures, which happen to
+ partially have the same structure than jmp_buf. However the
+ ucontext returned by getcontext, and thus the jmp_buf structure
+ returned by setjmp, contains the context of the trap instruction
+ in the glibc __[sig]setjmp wrapper, not the context of the user
+ code calling setjmp.
+
+ %o7 in the jmp_buf structure is stored at offset 18*8 in the
+ mc_gregs array, which is itself located at offset 32 into
+ jmp_buf. See bits/setjmp.h. This register contains the address
+ of the 'call setjmp' instruction in user code.
+
+ In order to determine the longjmp target address in the
+ initiating frame we need to examine the call instruction itself,
+ in particular whether the annul bit is set. If it is not set
+ then we need to jump over the instruction at the delay slot. */
+
+ if (target_read_memory (jb_addr + 32 + (18 * 8), buf, 8))
+ return 0;
+
+ *pc = extract_unsigned_integer (buf, 8, gdbarch_byte_order (gdbarch));
+
+ if (!sparc_is_annulled_branch_insn (*pc))
+ *pc += 4; /* delay slot insn */
+ *pc += 4; /* call insn */
+
+ return 1;
+}
+
+
static void
sparc64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
@@ -272,6 +320,9 @@
/* Make sure we can single-step over signal return system calls. */
tdep->step_trap = sparc64_linux_step_trap;
+ /* Make sure we can single-step over longjmp calls. */
+ set_gdbarch_get_longjmp_target (gdbarch, sparc64_linux_get_longjmp_target);
+
set_gdbarch_write_pc (gdbarch, sparc64_linux_write_pc);
/* Functions for 'catch syscall'. */