[release-branch.r58] ld: dwarf emit filenames in debug_line header instead of as...

««« CL 4609043 / caaab1e64d49
ld: dwarf emit filenames in debug_line header instead of as extended opcodes.

Makes it possible for older tools like objdump to find the filenames,
fixes  objdump -d -l --start-address=0x400c00 --stop-address=0x400c36 6.out
fixes #1950

R=rsc
CC=golang-dev
https://golang.org/cl/4609043
»»»

R=rsc
CC=golang-dev
https://golang.org/cl/4648068

diff --git a/src/cmd/ld/dwarf.c b/src/cmd/ld/dwarf.c
index 1721def678486a303ee31305518252df6110428d..50b42183e89b3762d4dd1c8f94d7c4bf7fd92971 100644 (file)
--- a/src/cmd/ld/dwarf.c
+++ b/src/cmd/ld/dwarf.c
@@ -1804,7 +1804,7 @@ mkvarname(char* name, int da)
 
 // flush previous compilation unit.
 static void
-flushunit(DWDie *dwinfo, vlong pc, vlong unitstart)
+flushunit(DWDie *dwinfo, vlong pc, vlong unitstart, int32 header_length)
 {
        vlong here;
 
@@ -1820,7 +1820,9 @@ flushunit(DWDie *dwinfo, vlong pc, vlong unitstart)
 
                here = cpos();
                seek(cout, unitstart, 0);
-               LPUT(here - unitstart - sizeof(int32));
+               LPUT(here - unitstart - sizeof(int32));  // unit_length
+               WPUT(3);  // dwarf version
+               LPUT(header_length); // header lenght starting here
                cflush();
                seek(cout, here, 0);
        }
@@ -1832,7 +1834,7 @@ writelines(void)
        Prog *q;
        Sym *s;
        Auto *a;
-       vlong unitstart, offs;
+       vlong unitstart, headerend, offs;
        vlong pc, epc, lc, llc, lline;
        int currfile;
        int i, lang, da, dt;
@@ -1842,6 +1844,7 @@ writelines(void)
        char *n, *nn;
 
        unitstart = -1;
+       headerend = -1;
        pc = 0;
        epc = 0;
        lc = 1;
@@ -1859,7 +1862,7 @@ writelines(void)
                // we're entering a new compilation unit
 
                if (inithist(s->autom)) {
-                       flushunit(dwinfo, epc, unitstart);
+                       flushunit(dwinfo, epc, unitstart, headerend - unitstart - 10);
                        unitstart = cpos();
 
                        if(debug['v'] > 1) {
@@ -1880,10 +1883,10 @@ writelines(void)
 
                        // Write .debug_line Line Number Program Header (sec 6.2.4)
                        // Fields marked with (*) must be changed for 64-bit dwarf
-                       LPUT(0);   // unit_length (*), will be filled in later.
+                       LPUT(0);   // unit_length (*), will be filled in by flushunit.
                        WPUT(3);   // dwarf version (appendix F)
-                       LPUT(11);  // header_length (*), starting here.
-
+                       LPUT(0);   // header_length (*), filled in by flushunit.
+                       // cpos == unitstart + 4 + 2 + 4
                        cput(1);   // minimum_instruction_length
                        cput(1);   // default_is_stmt
                        cput(LINE_BASE);     // line_base
@@ -1894,17 +1897,15 @@ writelines(void)
                        cput(1);   // standard_opcode_lengths[3]
                        cput(1);   // standard_opcode_lengths[4]
                        cput(0);   // include_directories  (empty)
-                       cput(0);   // file_names (empty) (emitted by DW_LNE's below)
-                       // header_length ends here.
 
                        for (i=1; i < histfilesize; i++) {
-                               cput(0);  // start extended opcode
-                               uleb128put(1 + strlen(histfile[i]) + 4);
-                               cput(DW_LNE_define_file);
                                strnput(histfile[i], strlen(histfile[i]) + 4);
                                // 4 zeros: the string termination + 3 fields.
                        }
 
+                       cput(0);   // terminate file_names.
+                       headerend = cpos();
+
                        pc = s->text->pc;
                        epc = pc;
                        currfile = 1;
@@ -2009,7 +2010,7 @@ writelines(void)
                dwfunc->hash = nil;
        }
 
-       flushunit(dwinfo, epc, unitstart);
+       flushunit(dwinfo, epc, unitstart, headerend - unitstart - 10);
        linesize = cpos() - lineo;
 }