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[avr-gcc-list] avr-gcc code generation and initialization of the return
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From: |
Torleif Sandnes |
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Subject: |
[avr-gcc-list] avr-gcc code generation and initialization of the return stack |
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Date: |
Wed, 05 May 2004 16:13:47 +0200 |
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User-agent: |
Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.5b) Gecko/20030901 Thunderbird/0.2 |
Hi.
While adding debug support for avr-gcc elf/dwarf object files in AVR Studio, we
have come upon a problem with some of the code generated by avr-gcc.
Quoting an e-mail from my colleague Svenn-Ivar:
It seems like the main function does an re-initialization of the return
stack (SPL/SPH). Actually, the new JTAGICE mkII expects the stack pointer
not to be modified this way apart from in the system startup-code, or the
single-stepping mechanisms wont work. The avr-gcc does set up the stack
properly in the startup-code, so I dont clearly see why it's done over again
in 'main'.
Do any of you know why the stack is reinitialized this way?
Can gcc's code egeneration be changed to not reinitialize the return stack?
Regards,
Torleif Sandnes
Here is a partial disassembly of an object file that illustrates the issue:
---------------------------------------------------------------------------
+00000000: 940C002E JMP 0x0000002E Jump
+00000002: 940C0049 JMP 0x00000049 Jump
+00000004: 940C0049 JMP 0x00000049 Jump
+00000006: 940C0049 JMP 0x00000049 Jump
+00000008: 940C0049 JMP 0x00000049 Jump
+0000000A: 940C0049 JMP 0x00000049 Jump
+0000000C: 940C0049 JMP 0x00000049 Jump
+0000000E: 940C0049 JMP 0x00000049 Jump
+00000010: 940C0049 JMP 0x00000049 Jump
+00000012: 940C0049 JMP 0x00000049 Jump
+00000014: 940C0049 JMP 0x00000049 Jump
+00000016: 940C0049 JMP 0x00000049 Jump
+00000018: 940C0049 JMP 0x00000049 Jump
+0000001A: 940C0049 JMP 0x00000049 Jump
+0000001C: 940C0049 JMP 0x00000049 Jump
+0000001E: 940C0049 JMP 0x00000049 Jump
+00000020: 940C0049 JMP 0x00000049 Jump
+00000022: 940C0049 JMP 0x00000049 Jump
+00000024: 940C0049 JMP 0x00000049 Jump
+00000026: 940C0049 JMP 0x00000049 Jump
+00000028: 940C0049 JMP 0x00000049 Jump
+0000002A: 940C0049 JMP 0x00000049 Jump
+0000002C: 940C0049 JMP 0x00000049 Jump
+0000002E: 2411 CLR R1 Exclusive OR
+0000002F: BE1F OUT 0x3F,R1 Out to I/O location
+00000030: EFCF SER R28 Load immediate
+00000031: E0D4 LDI R29,0x04 Load immediate
+00000032: BFDE OUT 0x3E,R29 Out to I/O location
+00000033: BFCD OUT 0x3D,R28 Out to I/O location
The previous four instructions set up the return stack for the first time
+00000034: E011 LDI R17,0x01 Load immediate
+00000035: E0A0 LDI R26,0x00 Load immediate
+00000036: E0B1 LDI R27,0x01 Load immediate
+00000037: EFE4 LDI R30,0xF4 Load immediate
+00000038: E0F0 LDI R31,0x00 Load immediate
+00000039: C002 RJMP +0x0002 Relative jump
+0000003A: 9005 LPM R0,Z+ Load program memory and
postincrement
+0000003B: 920D ST X+,R0 Store indirect and
postincrement
+0000003C: 30A0 CPI R26,0x00 Compare with immediate
+0000003D: 07B1 CPC R27,R17 Compare with carry
+0000003E: F7D9 BRNE -0x05 Branch if not equal
+0000003F: E011 LDI R17,0x01 Load immediate
+00000040: E0A0 LDI R26,0x00 Load immediate
+00000041: E0B1 LDI R27,0x01 Load immediate
+00000042: C001 RJMP +0x0001 Relative jump
+00000043: 921D ST X+,R1 Store indirect and
postincrement
+00000044: 30A0 CPI R26,0x00 Compare with immediate
+00000045: 07B1 CPC R27,R17 Compare with carry
+00000046: F7E1 BRNE -0x04 Branch if not equal
+00000047: 940C0066 JMP 0x00000066 Jump
+00000049: 940C0000 JMP 0x00000000 Jump
@0000004B: delay
17: {
+0000004B: 93CF PUSH R28 Push register on stack
+0000004C: 93DF PUSH R29 Push register on stack
+0000004D: B7CD IN R28,0x3D In from I/O location
+0000004E: B7DE IN R29,0x3E In from I/O location
+0000004F: 9722 SBIW R28,0x02 Subtract immediate from word
+00000050: B60F IN R0,0x3F In from I/O location
+00000051: 94F8 CLI Flag clear
+00000052: BFDE OUT 0x3E,R29 Out to I/O location
+00000053: BE0F OUT 0x3F,R0 Out to I/O location
+00000054: BFCD OUT 0x3D,R28 Out to I/O location
19: while(++i); // sleep until i wraps
+00000055: 8189 LDD R24,Y+1 Load indirect with
displacement
+00000056: 819A LDD R25,Y+2 Load indirect with
displacement
+00000057: 9601 ADIW R24,0x01 Add immediate to word
+00000058: 8389 STD Y+1,R24 Store indirect with
displacement
+00000059: 839A STD Y+2,R25 Store indirect with
displacement
+0000005A: 9700 SBIW R24,0x00 Subtract immediate from word
+0000005B: F009 BREQ +0x01 Branch if equal
19: while(++i); // sleep until i wraps
+0000005C: CFF8 RJMP -0x0008 Relative jump
+0000005D: 9622 ADIW R28,0x02 Add immediate to word
+0000005E: B60F IN R0,0x3F In from I/O location
+0000005F: 94F8 CLI Flag clear
+00000060: BFDE OUT 0x3E,R29 Out to I/O location
+00000061: BE0F OUT 0x3F,R0 Out to I/O location
+00000062: BFCD OUT 0x3D,R28 Out to I/O location
+00000063: 91DF POP R29 Pop register from stack
+00000064: 91CF POP R28 Pop register from stack
+00000065: 9508 RET Subroutine return
@00000066: main
35: {
+00000066: EECB LDI R28,0xEB Load immediate
+00000067: E0D4 LDI R29,0x04 Load immediate
+00000068: BFDE OUT 0x3E,R29 Out to I/O location
+00000069: BFCD OUT 0x3D,R28 Out to I/O location
The previous four instructions set up the return stack a second time^^
41: int counter = 0;
+0000006A: 8A1B STD Y+19,R1 Store indirect with
displacement
+0000006B: 8A1C STD Y+20,R1 Store indirect with
displacement
43: DDRB = 0xff;
+0000006C: EF8F SER R24 Load immediate
+0000006D: 93800024 STS 0x0024,R24 Store direct to data space
50: PORTB = 0xaa;
+0000006F: EA8A LDI R24,0xAA Load immediate
+00000070: 93800025 STS 0x0025,R24 Store direct to data space
51: delay();
+00000072: 940E004B CALL 0x0000004B Call subroutine
52: PORTB = 0x55;
+00000074: E585 LDI R24,0x55 Load immediate
+00000075: 93800025 STS 0x0025,R24 Store direct to data space
53: delay();
+00000077: 940E004B CALL 0x0000004B Call subroutine
+00000079: CFF5 RJMP -0x000B Relative jump
- [avr-gcc-list] avr-gcc code generation and initialization of the return stack,
Torleif Sandnes <=
- [avr-gcc-list] Re: avr-gcc code generation and initialization of the return stack, Theodore A. Roth, 2004/05/05
- [avr-gcc-list] Re: avr-gcc code generation and initialization of the return stack, Marek Michalkiewicz, 2004/05/05
- Re: [avr-gcc-list] avr-gcc code generation and initialization of the return stack, Julius Luukko, 2004/05/06
- Re: [avr-gcc-list] avr-gcc code generation and initialization of the return stack, Torleif Sandnes, 2004/05/07
- RE: [avr-gcc-list] avr-gcc code generation and initialization of the return stack, Larry Barello, 2004/05/07
- Re: [avr-gcc-list] avr-gcc code generation and initialization of the return stack, Brian Dean, 2004/05/08
- Re: [avr-gcc-list] avr-gcc code generation and initialization of the return stack, Jeff Barlow, 2004/05/08
- Re: [avr-gcc-list] avr-gcc code generation and initialization of the return stack, Julius Luukko, 2004/05/10
- Re: [avr-gcc-list] avr-gcc code generation and initialization of the return stack, Torleif Sandnes, 2004/05/13