segfault with backtrace and information

[Peter Jay Salzman <p@dirac.org>]

dosemu consistantly segfaults on one of my machines.

i'm using version 1.1.3.7 with the experimental sound patches under
vanilla 2.4.20.  machine arch is AMD athlon 1st generation 1.4 GHz with
a 1st generation ATI radeon.

the machine didn't oops.

backtrace is follows:

   lucifer# gdb /usr/local/bin/dos-debug 
   (gdb) run
   Starting program: /usr/local/bin/dos-debug 
   Linux kernel 2.4.19; CPU speed is 1300264000 Hz
   Dosemu-1.1.3.7 Running on CPU=586, FPU=1
   
   Program received signal SIGSEGV, Segmentation fault.
   0x080aeda4 in real_yylex (yylval=0x4d003b) at lexer.l:707
   707                                     yylval->s_value = strdup(&yytext[1]);
   (gdb) bt
   #0  0x080aeda4 in real_yylex (yylval=0x4d003b) at lexer.l:707
   #1  0x08107251 in _IO_stdin_used ()

the area of code:

   (gdb) l 707
   702     {STRQUOTELESS}          MAY_BEFORME {
   703                               yylval->s_value = strdup(yytext);
   704                               EXPRTYPE(yylval->s_value) = TYPE_STRQUOTELESS;
   705                               return(STRING); }
   706     ${IDENT}                MAY_BE {
   707                                     yylval->s_value = strdup(&yytext[1]);
   708                                     EXPRTYPE(yylval->s_value) =
   TYPE_STRQUOTELESS;
   709                                     return(VARIABLE);
   710                             }
   711     $${IDENT}               MAY_BE { enter_macrofile(&yytext[2]);}

   (gdb) printf "%s", &yytext[1]
   _DOSEMU_ORIG_PATH(gdb) 
   
   (gdb) printf "%s", strdup(&yytext[1])
   _DOSEMU_ORIG_PATH(gdb) 
   
   (gdb) printf "%s", yylval->s_value
   Cannot access memory at address 0x4d003b
   
   (gdb) printf "%s", yylval->s_value
   Cannot access memory at address 0x4d003b
   
   (gdb) ptype yylval->s_value
   type = char *
   
   (gdb) p yylval->s_value = strdup(&yytext[1]) 
   Cannot access memory at address 0x4d003b

i'm a bit confused at this point.  it looks like the address returned by
strdup is no good, but i have no idea how that can be.

strace provides no help:

   write(2, "Linux kernel 2.4.19; CPU speed i"..., 48) = 48
   write(2, "Dosemu-1.1.3.7 Running on CPU=58"..., 41) = 41
   brk(0x832d000)                          = 0x832d000
   --- SIGSEGV (Segmentation fault) ---
   +++ killed by SIGSEGV +++

ltrace output pretty much confirms what the backtrace said:

   strcmp("parser_version_3", "h_lucifer")           = 8
   strcmp("parser_version_3", "c_all")               = 13
   strcmp("parser_version_3", "parser_version_3")    = 0
   strchr(""/etc/dosemu.conf"", '\n')                = NULL
   __strdup(0x08329490, 10, 0, 0x080aa782, 0x08107251) = 0x0832cb78
   --- SIGSEGV (Segmentation fault) ---
   +++ killed by SIGSEGV +++


dosemu works fine on my other machines.  this seems to be a problem with
this machine only, but nothing about this looks arch dependent to me.

any suggestions?

pete


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