[binutils-gdb] Avoid infinite recursion in find_pc_sect_line

[binutils-gdb] Avoid infinite recursion in find_pc_sect_line

[Kevin Buettner]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=dd69bf7a78a489783c397f2552eeb7999defcb6a

commit dd69bf7a78a489783c397f2552eeb7999defcb6a
Author: Kevin Buettner <kevinb@redhat.com>
Date:   Sun Nov 17 11:37:39 2019 -0700

    Avoid infinite recursion in find_pc_sect_line
    
    A patch somewhat like this patch has been in Fedora GDB for well over
    a decade.  The Fedora patch was written by Jan Kratochvil.  The Fedora
    version prints a warning and attempts to continue.  This version will
    error out, fatally.  An earlier version of this patch was more like
    the Fedora version than this one.  Simon Marchi recommended use of an
    assertion to test for the infinite recursion; I decided to use an
    explicit test (with an "if" statement) along with a call to
    internal_error() if the condition is met.  This way, I could include
    a plea to file a bug report.
    
    It was motivated by a customer reported bug (back in 2006!) which
    showed infinite mutual recursion between find_pc_sect_line and
    find_pc_line.  Here is a portion of the backtrace from the bug report:
    
        (gdb) bt
        #0  0x00000000004450a4 in lookup_minimal_symbol_by_pc_section (
            pc=251700325328, section=0x570f500) at gdb/minsyms.c:484
        #1  0x00000000004bbfb2 in find_pc_sect_line (pc=251700325328,
            section=0x570f500, notcurrent=0) at gdb/symtab.c:2057
        #2  0x00000000004bc480 in find_pc_line (pc=251700325328, notcurrent=0)
            at gdb/symtab.c:2232
        #3  0x00000000004bc1ff in find_pc_sect_line (pc=251700325328,
            section=0x570f500, notcurrent=0) at gdb/symtab.c:2081
    
        ...   (lots and lots of the same two functions with the same parameters)
    
        #1070 0x00000000004bc480 in find_pc_line (pc=251700325328, notcurrent=0)
            at gdb/symtab.c:2232
        #1071 0x00000000004bc1ff in find_pc_sect_line (pc=251700325328,
            section=0x570f500, notcurrent=0) at gdb/symtab.c:2081
        #1072 0x00000000004bc480 in find_pc_line (pc=251700325328, notcurrent=0)
            at gdb/symtab.c:2232
        #1073 0x00000000004bc1ff in find_pc_sect_line (pc=251700325328,
            section=0x570f500, notcurrent=0) at gdb/symtab.c:2081
        #1074 0x00000000004bc480 in find_pc_line (pc=251700325328, notcurrent=0)
            at gdb/symtab.c:2232
        #1075 0x00000000004bc1ff in find_pc_sect_line (pc=251696794399,
            section=0x59b0df8, notcurrent=0) at gdb/symtab.c:2081
        #1076 0x00000000004bc480 in find_pc_line (pc=251696794399, notcurrent=0)
            at gdb/symtab.c:2232
        #1077 0x000000000055550e in find_frame_sal (frame=0xb3f3e0, sal=0x7fff1d1a8200)
            at gdb/frame.c:1392
        #1078 0x00000000004d86fd in set_current_sal_from_frame (frame=0x1648, center=1)
            at gdb/stack.c:379
        #1079 0x00000000004cf137 in normal_stop () at gdb/infrun.c:3147
        ...
    
    The test case was a large application.  Attempts were made to make a
    small(er) test case, but those attempts were not successful.
    Therefore, I cannot provide a new test for this patch.
    
    That said, we ought to guard against recursively calling
    find_pc_sect_line (via find_pc_line) with the identical PC value that
    it had been called with.  Should this happen, infinite recursion (as
    shown in the above backtrace) is the result.  This patch prevents
    that from happening.
    
    If this should happens, there is a bug somewhere, perhaps in GDB, perhaps
    in some other part of the toolchain or a library.  We error out fatally
    with a message briefly describing the condition along with a plea to file
    a bug report.
    
    I spent some time looking at the surrounding code and commentary which
    handle the case of PC being in a stub/trampoline.  It first appeared
    in the public GDB repository in April, 1999.  The ChangeLog entry for
    this commit is from 1998-12-31.  The relevant portion is:
    
            (find_pc_sect_line): Return correct information if pc is in import
            or export stub (trampoline).
    
    What's remarkable about the overall ChangeLog entry is that it's over
    2500+ lines long!  I believe that this was part of the infamous "HP
    merge" (in which insufficient due diligence was given in accepting
    a large batch of changes from an outside source).  In the years that
    followed, much of this code was either significantly revised or
    outright removed.
    
    For this particular case, I'm grateful that extensive comments were
    provided by "RT".  (I haven't been able to figure out who RT is/was.)
    I've decided against attempting to revise this stub/trampoline handling
    code any further than adding Jan's test which prevents an obvious case
    of infinite recursion.
    
    I've tested on Fedora 31, x86-64.  I see no regressions.  I've also
    searched the logfile for the new message, but as expected, no message
    was found (which is good).
    
    gdb/ChangeLog:
    
            * symtab.c (find_pc_sect_line): Add check which prevents infinite
            recursion.
    
    Change-Id: I595470be6ab5f61ca7e4e9e70c61a252c0deaeaa

Diff:
---
 gdb/ChangeLog |  5 +++++
 gdb/symtab.c  | 12 +++++++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index e8fc63cc25a..f6bd31cb4c7 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-11  Kevin Buettner  <kevinb@redhat.com>
+
+	* symtab.c (find_pc_sect_line): Add check which prevents infinite
+	recursion.
+	
 2020-03-11  Simon Marchi  <simon.marchi@efficios.com>
 
 	* configure: Re-generate.
diff --git a/gdb/symtab.c b/gdb/symtab.c
index 44b711397d5..aa415a93999 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -3158,7 +3158,17 @@ find_pc_sect_line (CORE_ADDR pc, struct obj_section *section, int notcurrent)
 	  ;
 	/* fall through */
 	else
-	  return find_pc_line (BMSYMBOL_VALUE_ADDRESS (mfunsym), 0);
+	  {
+	    /* Detect an obvious case of infinite recursion.  If this
+	       should occur, we'd like to know about it, so error out,
+	       fatally.  */
+	    if (BMSYMBOL_VALUE_ADDRESS (mfunsym) == pc)
+	      internal_error (__FILE__, __LINE__,
+	        _("Infinite recursion detected in find_pc_sect_line;"
+		  "please file a bug report"));
+
+	    return find_pc_line (BMSYMBOL_VALUE_ADDRESS (mfunsym), 0);
+	  }
       }
 
   symtab_and_line val;