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rs6000-tdep.c:skip_prologue avoid negative left shift

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the rs6000-tdep.c::skip_prologue function has the following code:

          unsigned int all_mask = ~((1U << fdata->saved_gpr) - 1);

          /* Not a recognized prologue instruction.
             Handle optimizer code motions into the prologue by continuing
             the search if we have no valid frame yet or if the return
             address is not yet saved in the frame.  Also skip instructions
             if some of the GPRs expected to be saved are not yet saved.  */
          if (fdata->frameless == 0 && fdata->nosavedpc == 0
              && (fdata->gpr_mask & all_mask) == all_mask)
            break;

The problem is that fdata->saved_gpr is initialized to -1, and so,
if no instruction is found in the function's prologue that causes us
to set that field to a non-negative value, the sanitizer crashes
with the following message:

    rs6000-tdep.c:1965:34: runtime error: shift exponent -1 is negative

This patch fixes the issue the by only doing the shift if saved_gpr
is not negative. When saved_gpr is negative, we actually don't need
the shift.

gdb/ChangeLog:

        * rs6000-tdep.c (skip_prologue): Fix potential negative left
        shifting.

Tested on ppc-linux native.
Also tested on ppc-elf (baremetal) using AdaCore's testsuite.
This commit is contained in:
Joel Brobecker 2018-11-01 16:46:05 -05:00
parent e1c3a37375
commit 1cc62f2e44
2 changed files with 12 additions and 4 deletions
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5
gdb/ChangeLog
View File

@ -1,3 +1,8 @@
2018-11-01 Joel Brobecker <brobecker@adacore.com>
* rs6000-tdep.c (skip_prologue): Fix potential negative left
shifting.
2018-11-01 Jerome Guitton <guitton@adacore.com> 2018-11-01 Jerome Guitton <guitton@adacore.com>
Joel Brobecker <brobecker@adacore.com> Joel Brobecker <brobecker@adacore.com>

11
gdb/rs6000-tdep.c
View File

@ -1975,16 +1975,19 @@ skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc, CORE_ADDR lim_pc,
else else
{ {
unsigned int all_mask = ~((1U << fdata->saved_gpr) - 1);
/* Not a recognized prologue instruction. /* Not a recognized prologue instruction.
Handle optimizer code motions into the prologue by continuing Handle optimizer code motions into the prologue by continuing
the search if we have no valid frame yet or if the return the search if we have no valid frame yet or if the return
address is not yet saved in the frame. Also skip instructions address is not yet saved in the frame. Also skip instructions
if some of the GPRs expected to be saved are not yet saved. */ if some of the GPRs expected to be saved are not yet saved. */
if (fdata->frameless == 0 && fdata->nosavedpc == 0 if (fdata->frameless == 0 && fdata->nosavedpc == 0
&& (fdata->gpr_mask & all_mask) == all_mask) && fdata->saved_gpr != -1)
break; {
unsigned int all_mask = ~((1U << fdata->saved_gpr) - 1);
if ((fdata->gpr_mask & all_mask) == all_mask)
break;
}
if (op == 0x4e800020 /* blr */ if (op == 0x4e800020 /* blr */
|| op == 0x4e800420) /* bctr */ || op == 0x4e800420) /* bctr */