Author: sewardj
Date: 2008-03-07 22:17:31 +0000 (Fri, 07 Mar 2008)
New Revision: 7590
Log:
Try to handle the situation where an object is first split into a base
object (without D3 info) and a debuginfo (with D3 info), and then the
base object is prelinked to some nonzero address, but the debuginfo
object is left unchanged. A nasty and unprincipled hack.
Modified:
trunk/coregrind/m_debuginfo/d3basics.c
trunk/coregrind/m_debuginfo/readdwarf3.c
Modified: trunk/coregrind/m_debuginfo/d3basics.c
===================================================================
--- trunk/coregrind/m_debuginfo/d3basics.c 2008-03-07 20:07:58 UTC (rev
7589)
+++ trunk/coregrind/m_debuginfo/d3basics.c 2008-03-07 22:17:31 UTC (rev
7590)
@@ -502,6 +502,10 @@
before pushing the result. FIXME: how can we be sure
the data bias is intended, not the text bias? I don't
know. */
+ /* Furthermore, do we need to take into account the
+ horrible prelinking-induced complications as described
+ in "Comment_Regarding_DWARF3_Text_Biasing" in
+ readdwarf3.c? Currently I don't know. */
PUSH( *(Addr*)expr + data_bias );
expr += sizeof(Addr);
break;
Modified: trunk/coregrind/m_debuginfo/readdwarf3.c
===================================================================
--- trunk/coregrind/m_debuginfo/readdwarf3.c 2008-03-07 20:07:58 UTC (rev
7589)
+++ trunk/coregrind/m_debuginfo/readdwarf3.c 2008-03-07 22:17:31 UTC (rev
7590)
@@ -478,9 +478,100 @@
VG_(printf)("}");
}
-static void bias_GX ( /*MOD*/GExpr* gx, Addr bias )
+/* "Comment_Regarding_DWARF3_Text_Biasing" (is referred to elsewhere)
+ -----------------------------------------------------------------
+ apply_kludgey_text_bias() is our mechanism for biasing text
+ addresses found in DWARF3 .debug_info, .debug_ranges, .debug_loc
+ sections. This is a nasty and unprincipled hack.
+
+ Biasing the text svmas, so as to obtain text avmas, should be
+ straightforward, right? We just add on di->text_bias, as
+ carefully computed by readelf.c.
+
+ That works OK most of the time. But in the following case it fails:
+ 1. The object is made in the usual way (gcc -g, etc)
+ 2. The DWARF3 stuff removed from it and parked in a .debuginfo object
+ 3. The remaining (base) object is then prelinked.
+
+ Prelinking changes the text svmas throughout an object by some
+ constant amount, including the DWARF3 stuff. So if the DWARF3
+ stuff remains attached to the original object, then there is no
+ problem. However, if the DWARF3 stuff is detached, and the
+ remaining object is prelinked and the debuginfo object isn't, then
+ we have a problem: the text bias computed for the main object
+ isn't correct for the debuginfo object.
+
+ So the following kludged is used to bias text svmas.
+
+ 1. First, try with the text bias computed for the main object. If
+ that gives an avma inside the area in which the text segment is
+ known to have been mapped, then all well and good.
+
+ 2. If not, try using the avma of the text mapped area as a bias.
+ Again, if that works out, fine. This is the heart of the
+ kludge. It implicitly treats the svma-s to be biased as if
+ they had been prelinked to zero.
+
+ 3. If even that doesn't work, just return the avma unchanged.
+
+ For each object/object-pair, we count the number of times each
+ case occurs. We flag an error (which the user gets to see) if (3)
+ ever occurs, or if a mixture of (1) and (2) occurs. That should
+ at least catch the most obvious snafus.
+
+ Caveats: the main remaining worry is whether this problem somehow
+ also affects the data-biasing done for case DW_OP_addr in
+ ML_(evaluate_Dwarf3_Expr) in d3basics.c. This is currently
+ unknown.
+
+ Possible sources of info: canonical description seems to be:
+
+ http://people.redhat.com/jakub/prelink.pdf
+
+ See para at line 337 starting "DWARF 2 debugging information ..."
+
+ This thread looks like the gdb people hitting the same issue:
+
+ http://sourceware.org/ml/gdb-patches/2007-01/msg00278.html
+*/
+typedef
+ struct {
+ /* FIXED */
+ Addr rx_map_avma;
+ SizeT rx_map_size;
+ OffT text_bias;
+ /* VARIABLE -- count stats */
+ UWord n_straightforward_biasings;
+ UWord n_kludgey_biasings;
+ UWord n_failed_biasings;
+ }
+ KludgeyTextBiaser;
+
+static Addr apply_kludgey_text_bias ( KludgeyTextBiaser* ktb,
+ Addr allegedly_text_svma ) {
+ Addr res;
+ res = allegedly_text_svma + ktb->text_bias;
+ if (res >= ktb->rx_map_avma
+ && res < ktb->rx_map_avma + ktb->rx_map_size) {
+ ktb->n_straightforward_biasings++;
+ return res;
+ }
+ res = allegedly_text_svma + ktb->rx_map_avma;
+ if (res >= ktb->rx_map_avma
+ && res < ktb->rx_map_avma + ktb->rx_map_size) {
+ ktb->n_kludgey_biasings++;
+ return res;
+ }
+ ktb->n_failed_biasings++;
+ return allegedly_text_svma; /* this svma is a luzer */
+}
+
+
+/* Apply a text bias to a GX. Kludgily :-( */
+static void bias_GX ( /*MOD*/GExpr* gx, KludgeyTextBiaser* ktb )
{
UShort nbytes;
+ Addr* pA;
UChar* p = &gx->payload[0];
UChar uc;
uc = *p++; /*biasMe*/
@@ -493,8 +584,15 @@
if (uc == 1)
break; /*isEnd*/
vg_assert(uc == 0);
- * ((Addr*)p) += bias; /*aMin*/ p += sizeof(Addr);
- * ((Addr*)p) += bias; /*aMax*/ p += sizeof(Addr);
+ /* t-bias aMin */
+ pA = (Addr*)p;
+ *pA = apply_kludgey_text_bias( ktb, *pA );
+ p += sizeof(Addr);
+ /* t-bias aMax */
+ pA = (Addr*)p;
+ *pA = apply_kludgey_text_bias( ktb, *pA );
+ p += sizeof(Addr);
+ /* nbytes, and actual expression */
nbytes = * (UShort*)p; p += sizeof(UShort);
p += nbytes;
}
@@ -2792,6 +2890,8 @@
Word i;
Bool td3 = di->trace_symtab;
XArray* /* of TempVar* */ dioff_lookup_tab;
+ Bool text_biasing_borked;
+ KludgeyTextBiaser ktb;
#if 0
/* This doesn't work properly because it assumes all entries are
@@ -3108,9 +3208,15 @@
TRACE_D3("\n");
TRACE_D3("------ Resolving type entries ------\n");
+ /* See "Comment_Regarding_DWARF3_Text_Biasing" above. */
+ VG_(memset)( &ktb, 0, sizeof(ktb ));
+ ktb.rx_map_avma = di->rx_map_avma;
+ ktb.rx_map_size = di->rx_map_size;
+ ktb.text_bias = di->text_bias;
+
resolve_type_entities( admin, tempvars );
for (gexpr = gexprs; gexpr; gexpr = gexpr->next) {
- bias_GX( gexpr, di->text_bias );
+ bias_GX( gexpr, &ktb );
}
TRACE_D3("\n");
@@ -3278,13 +3384,19 @@
vg_assert(pcMax < ~(Addr)0);
}
- if (i > 0 && (i%2) == 0) TRACE_D3("\n ");
+ /* Apply text biasing, for non-global variables. */
+ if (varp->level > 0) {
+ pcMin = apply_kludgey_text_bias( &ktb, pcMin );
+ pcMax = apply_kludgey_text_bias( &ktb, pcMax );
+ }
+
+ if (i > 0 && (i%2) == 0)
+ TRACE_D3("\n ");
TRACE_D3("[%p,%p] ", pcMin, pcMax );
ML_(addVar)(
di, varp->level,
- pcMin + (varp->level==0 ? 0 : di->text_bias),
- pcMax + (varp->level==0 ? 0 : di->text_bias),
+ pcMin, pcMax,
varp->name, (void*)varp->typeR,
varp->gexpr, varp->fbGX,
varp->fName, varp->fLine, td3
@@ -3296,6 +3408,27 @@
/* and move on to the next var */
}
+ /* For the text biasing to work out, we expect that:
+ - there were no failures, and
+ - either all were done straightforwardly, or all kludgily,
+ but not with a mixture
+ */
+ text_biasing_borked
+ = ktb.n_failed_biasings > 0
+ || (ktb.n_straightforward_biasings > 0 && ktb.n_kludgey_biasings > 0);
+
+ if (td3 || text_biasing_borked) {
+ VG_(printf)("TEXT SVMA BIASING STATISTICS:\n");
+ VG_(printf)(" straightforward biasings: %lu\n",
+ ktb.n_straightforward_biasings );
+ VG_(printf)(" kludgey biasings: %lu\n",
+ ktb.n_kludgey_biasings );
+ VG_(printf)(" failed biasings: %lu\n\n",
+ ktb.n_failed_biasings );
+ }
+ if (text_biasing_borked)
+ barf("couldn't make sense of DWARF3 text-svma biasing; details above");
+
/* Now free all the TempVars */
for (varp = tempvars; varp; varp = varp2) {
varp2 = varp->next;
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