st-util: wrong register values passed to gdb (st-link v2)

[arsv]

• Programmer/board type: Stlink v2 clone
• Operating system and version: Linux
• Stlink tools git commit hash: 5c03678
• Stlink commandline tool name: st-util
• Target chip: STM32F103CBT6 (Maple Mini clone)

Test code on the target device:

initial_stack_ptr:
        .word 0x20005000
interrupt_vectors:
        .word reset_handler + 1
        ...
reset_handler:
        mov r0, #0
        mov r1, #1
        mov r2, #2
        mov r3, #3
        mov r4, #4
        mov r5, #5
        mov r6, #6
        mov r7, #7
        mov r8, #8
        mov r9, #9
        mov r10, #10
        mov r11, #11
        mov r12, #12
        mov r14, #14
1:      b.n 1b

Actual GDB output with the target stopped on the final line of the test code:

(gdb) info reg
r0             0x30                48
r1             0x30                48
r2             0xbbc56fb8          3150278584
r3             0x7ffe              32766
r4             0x3                 3
r5             0x4                 4
r6             0x5                 5
r7             0x6                 6
r8             0x7                 7
r9             0x8                 8
r10            0x9                 9
r11            0xa                 10
r12            0xb                 11
sp             0xc                 0xc
lr             0x20005000          536891392
pc             0xe                 0xe
cpsr           0x1000000           16777216

Expected GDB output in the same scenario:

(gdb) info reg
r0             0x0                 0
r1             0x1                 1
r2             0x2                 2
r3             0x3                 3
r4             0x4                 4
r5             0x5                 5
r6             0x6                 6
r7             0x7                 7
r8             0x8                 8
r9             0x9                 9
r10            0xa                 10
r11            0xb                 11
r12            0xc                 12
sp             0x20005000          ...
lr             0xe                 14
pc             ....                ...
cpsr           ....                ...

Adding debug output to stlink_read_all_regs() confirms that the culprit is in fact st-util, not gdb:

int reg_offset = sl->version.jtag_api == STLINK_JTAG_API_V1 ? 0 : 4;
sl->q_len = (int)size;
stlink_print_data(sl);

for (i = reg_offset; i < 16; i++) regp->r[i] = read_uint32(sl->q_buf, i * 4);

DLOG("reg_offset=%i\n", reg_offset);
DLOG("r0 %08X r4 %08X   r8 %08X r12 %08X\n", regp->r[0], regp->r[4], regp->r[8],  regp->r[12]);
DLOG("r1 %08X r5 %08X   r9 %08X r13 %08X\n", regp->r[1], regp->r[5], regp->r[9],  regp->r[13]);
DLOG("r2 %08X r6 %08X  r10 %08X r14 %08X\n", regp->r[2], regp->r[6], regp->r[10], regp->r[14]);
DLOG("r3 %08X r7 %08X  r11 %08X r15 %08X\n", regp->r[3], regp->r[7], regp->r[11], regp->r[15]);

Output of the code above:

2020-09-09T23:31:58 DEBUG usb.c: reg_offset=4
2020-09-09T23:31:58 DEBUG usb.c: r0 00000030 r4 00000003   r8 00000007 r12 0000000B
2020-09-09T23:31:58 DEBUG usb.c: r1 00000030 r5 00000004   r9 00000008 r13 0000000C
2020-09-09T23:31:58 DEBUG usb.c: r2 D81F1598 r6 00000005  r10 00000009 r14 20005000
2020-09-09T23:31:58 DEBUG usb.c: r3 00007FFE r7 00000006  r11 0000000A r15 0000000E
2020-09-09T23:31:58 DEBUG gdb-server.c: send: 300000003000000098151fd8fe7f0000030000000400000005000000060000000700000008000000090000000a0000000b0000000c000000005000200e000000

I'm going to send a PR for this but that patch will probably require some context.