I am using Atmel Studio to develop a project using the SAM D21. I recently downloaded GCC 9.3.1 from the ARM web site because I need C++17 (not supported on GCC 6.3.1 that comes with Atmel Studio). When I'm in the Atmel Studio debugger, I find the live disassembly has large swaths of "No source file". The effect of that is to make it very difficult to step and set breakpoints because the debugger can't find the machine code for a given source line. If I switch back to the older GCC, this issue generally goes away. The disassembly produced by objdump has no gaps in the source code, so the info must still be present in the object file.
Here's a specific snippet, first the from the listing file produced by objdump:
if (ch >= 'A' && ch <= 'Z')
134e: 0003 movs r3, r0
1350: 3b41 subs r3, #65 ; 0x41
1352: b2db uxtb r3, r3
1354: 2b19 cmp r3, #25
1356: d801 bhi.n 135c <main+0x1f8>
ch += 'a' - 'A';
1358: 3020 adds r0, #32
135a: b2c0 uxtb r0, r0
switch (ch)
135c: 2877 cmp r0, #119 ; 0x77
135e: d106 bne.n 136e <main+0x20a>
case 'w':
// Trigger WDT
DEBUG_PRINT("Triggering WDT\n");
1360: 4864 ldr r0, [pc, #400] ; (14f4 <main+0x390>)
1362: f000 fbd3 bl 1b0c <puts>
for (;;);
1366: e7fe b.n 1366 <main+0x202>
iTmp &= ~ID_Right;
1368: 2205 movs r2, #5
136a: 4393 bics r3, r2
136c: e7ab b.n 12c6 <main+0x162>
But the disassembly in the debugger looks like this:
if (ch >= 'A' && ch <= 'Z') 0000134E 03.00 movs r3, r0 00001350 41.3b subs r3, #65 --- No source file ------------------------------------------------------------- 00001352 db.b2 uxtb r3, r3 00001354 19.2b cmp r3, #25 00001356 01.d8 bhi #2 00001358 20.30 adds r0, #32 0000135A c0.b2 uxtb r0, r0 0000135C 77.28 cmp r0, #119 0000135E 06.d1 bne #12 00001360 64.48 ldr r0, [pc, #400] 00001362 00.f0.d3.fb bl #1958 00001366 fe.e7 b #-4 00001368 05.22 movs r2, #5 0000136A 93.43 bics r3, r2 0000136C ab.e7 b #-170
Does anyone know if there's been a change in the debugging info emitted by the compiler? Might there be a GCC command option that could fix this? I have built tools that dig into DWARF format, so I could potentially make one that modified the debug info if that's what it took.
