[gdb/symtab] Make find_block_in_blockvector more robust

While working on PR25858 I noticed that the following trigger patch:
...
@@ -2918,6 +2918,7 @@ find_pc_sect_compunit_symtab
          const struct blockvector *bv;

          bv = COMPUNIT_BLOCKVECTOR (cust);
+         (volatile int)blockvector_contains_pc (bv, pc);
          b = BLOCKVECTOR_BLOCK (bv, GLOBAL_BLOCK);

          if (BLOCK_START (b) <= pc
...
triggers this assert, which checks that the returned block indeed
contains pc:
...
@@ -170,7 +170,10 @@ find_block_in_blockvector

     {
       b = BLOCKVECTOR_BLOCK (bl, bot);
       if (BLOCK_END (b) > pc)
-       return b;
+       {
+         gdb_assert (BLOCK_START (b) <= pc);
+         return b;
+       }
       bot--;
     }

...
when running test-case gdb.ada/bp_c_mixed_case.exp.

It's possible that the trigger patch breaks an undocumented invariant:  I've
tried a build and test run without the trigger patch and did not manage to
trigger the assert.

For robustness-sake, fix the assert by bailing out if 'BLOCK_START (b) <= pc'
doesn't hold.

Tested on x86_64-linux.

gdb/ChangeLog:

2020-10-22  Tom de Vries  <tdevries@suse.de>

	* block.c (find_block_in_blockvector): Make sure the returned block
	contains pc.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index bda88839b8dddcf2759d975024ab320058bcb255..76c5e9e8af3cf856acfe99cf294947b3248245cf 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2020-10-22  Tom de Vries  <tdevries@suse.de>
+
+       * block.c (find_block_in_blockvector): Make sure the returned block
+       contains pc.
+
 2020-10-22  Simon Marchi  <simon.marchi@polymtl.ca>
 
        PR gdb/26693

diff --git a/gdb/block.c b/gdb/block.c
index 597d6d5d875a9b7a12af20d9e9780b42deef4ef3..070d3f77697778ab49e29cf0aba580b57bac2822 100644 (file)
--- a/gdb/block.c
+++ b/gdb/block.c
@@ -166,6 +166,8 @@ find_block_in_blockvector (const struct blockvector *bl, CORE_ADDR pc)
   while (bot >= STATIC_BLOCK)
     {
       b = BLOCKVECTOR_BLOCK (bl, bot);
+      if (!(BLOCK_START (b) <= pc))
+       return NULL;
       if (BLOCK_END (b) > pc)
        return b;
       bot--;