aboutsummaryrefslogtreecommitdiff
path: root/gas/write.c
diff options
context:
space:
mode:
authorAlan Modra <amodra@gmail.com>2007-03-14 11:03:38 +0000
committerAlan Modra <amodra@gmail.com>2007-03-14 11:03:38 +0000
commitd1c5f15864c27771719a259e07207de35d9154eb (patch)
treea35a5b38bc27a52f4d2cfeb0a9678b1a24fb17e2 /gas/write.c
parentd796c0adf2056973411ac806b06661eaa3563eed (diff)
downloadgdb-d1c5f15864c27771719a259e07207de35d9154eb.zip
gdb-d1c5f15864c27771719a259e07207de35d9154eb.tar.gz
gdb-d1c5f15864c27771719a259e07207de35d9154eb.tar.bz2
PR 4029
* write.c (relax_segment): Insert extra alignment padding to break infinite relax loop when given impossible gcc_except_table assembly.
Diffstat (limited to 'gas/write.c')
-rw-r--r--gas/write.c97
1 files changed, 90 insertions, 7 deletions
diff --git a/gas/write.c b/gas/write.c
index b94099b..df858a3 100644
--- a/gas/write.c
+++ b/gas/write.c
@@ -1960,13 +1960,38 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
/* Do relax(). */
{
unsigned long max_iterations;
- offsetT stretch; /* May be any size, 0 or negative. */
- /* Cumulative number of addresses we have relaxed this pass.
- We may have relaxed more than one address. */
- int stretched; /* Have we stretched on this pass? */
- /* This is 'cuz stretch may be zero, when, in fact some piece of code
- grew, and another shrank. If a branch instruction doesn't fit anymore,
- we could be scrod. */
+
+ /* Cumulative address adjustment. */
+ offsetT stretch;
+
+ /* Have we made any adjustment this pass? We can't just test
+ stretch because one piece of code may have grown and another
+ shrank. */
+ int stretched;
+
+ /* Most horrible, but gcc may give us some exception data that
+ is impossible to assemble, of the form
+
+ .align 4
+ .byte 0, 0
+ .uleb128 end - start
+ start:
+ .space 128*128 - 1
+ .align 4
+ end:
+
+ If the leb128 is two bytes in size, then end-start is 128*128,
+ which requires a three byte leb128. If the leb128 is three
+ bytes in size, then end-start is 128*128-1, which requires a
+ two byte leb128. We work around this dilemma by inserting
+ an extra 4 bytes of alignment just after the .align. This
+ works because the data after the align is accessed relative to
+ the end label.
+
+ This counter is used in a tiny state machine to detect
+ whether a leb128 followed by an align is impossible to
+ relax. */
+ int rs_leb128_fudge = 0;
/* We want to prevent going into an infinite loop where one frag grows
depending upon the location of a symbol which is in turn moved by
@@ -2089,6 +2114,49 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
}
growth = newoff - oldoff;
+
+ /* If this align happens to follow a leb128 and
+ we have determined that the leb128 is bouncing
+ in size, then break the cycle by inserting an
+ extra alignment. */
+ if (growth < 0
+ && (rs_leb128_fudge & 16) != 0
+ && (rs_leb128_fudge & 15) >= 2)
+ {
+ segment_info_type *seginfo = seg_info (segment);
+ struct obstack *ob = &seginfo->frchainP->frch_obstack;
+ struct frag *newf;
+
+ newf = frag_alloc (ob);
+ obstack_blank_fast (ob, fragP->fr_var);
+ obstack_finish (ob);
+ memcpy (newf, fragP, SIZEOF_STRUCT_FRAG);
+ memcpy (newf->fr_literal,
+ fragP->fr_literal + fragP->fr_fix,
+ fragP->fr_var);
+ newf->fr_type = rs_fill;
+ newf->fr_fix = 0;
+ newf->fr_offset = (((offsetT) 1 << fragP->fr_offset)
+ / fragP->fr_var);
+ if (newf->fr_offset * newf->fr_var
+ != (offsetT) 1 << fragP->fr_offset)
+ {
+ newf->fr_offset = (offsetT) 1 << fragP->fr_offset;
+ newf->fr_var = 1;
+ }
+ /* Include growth of new frag, because rs_fill
+ frags don't normally grow. */
+ growth += newf->fr_offset * newf->fr_var;
+ /* The new frag address is newoff. Adjust this
+ for the amount we'll add when we process the
+ new frag. */
+ newf->fr_address = newoff - stretch - growth;
+ newf->relax_marker ^= 1;
+ fragP->fr_next = newf;
+#ifdef DEBUG
+ as_warn (_("padding added"));
+#endif
+ }
}
break;
@@ -2228,8 +2296,23 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
{
stretch += growth;
stretched = 1;
+ if (fragP->fr_type == rs_leb128)
+ rs_leb128_fudge += 16;
+ else if (fragP->fr_type == rs_align
+ && (rs_leb128_fudge & 16) != 0
+ && stretch == 0)
+ rs_leb128_fudge += 16;
+ else
+ rs_leb128_fudge = 0;
}
}
+
+ if (stretch == 0
+ && (rs_leb128_fudge & 16) == 0
+ && (rs_leb128_fudge & -16) != 0)
+ rs_leb128_fudge += 1;
+ else
+ rs_leb128_fudge = 0;
}
/* Until nothing further to relax. */
while (stretched && -- max_iterations);