Retrieve message id from PASE signal handler

instructions.md

gcc -std=c99 -o pase-signal-msgid pase-signal-msgid.c && ./pase-signal-msgid

Example output:

ptr: ffffffffffffba1
----- in handler -----
msgid = MCH0602

pase-signal-msgid.c

#include <stdio.h>     
#include <stdlib.h>
#include <as400_protos.h>
#include <os400msg.h>

void fast_e2a(char* src, size_t src_len);

typedef struct Qus_EC
{
    int  Bytes_Provided;
    int  Bytes_Available;
    char Exception_Id[7];
    char Reserved;
     /*char Exception_Data[];*/           /* Varying length        */
} Qus_EC_t;

void  handler(int sig, siginfo_t* info, void* ucontext)
{
    ucontext_t_os400* ctx = ucontext;
    
    Qmh_Rcvm_RCVM0100_t msg;
    Qus_EC_t err = { sizeof(err) };

    printf("----- in handler -----\n");

    int rc = QMHRCVPM(
        &msg,
        sizeof(msg),
        "RCVM0100",
        "*",
        0,
        "*ANY",
        &ctx->msgkey,
        0,
        "*SAME",
        &err
    );

    msg.Message_Id[7] = 0;
    fast_e2a(msg.Message_Id, sizeof(msg.Message_Id));

    printf("msgid = %s\n", rc, msg.Message_Id);

    exit(1);
}

int main(int argc, char *argv[])    
{    
    struct sigaction sa;
    sa.sa_sigaction = &handler;
    sa.sa_flags = SA_SIGINFO;

    sigaction(SIGSEGV, &sa, NULL);
    
    char buf[17];

    // Ensure our ILE pointer is mis-aligned
    int offset = ~((unsigned long)&buf[0]) & 0xF ? 1 : 0;
    ILEpointer* ptr = (ILEpointer*) &buf[offset];

    printf("ptr: %p\n", ptr);

    _RSLOBJ2(ptr, RSLOBJ_TS_PGM, "QP2TERM", "QSYS");
    return 0;
}


// this is the 37 to 1252 conversion table.
static const unsigned char e2a_table[256] =
{
    0x00,0x01,0x02,0x03,0x9c,0x09,0x86,0x7f,0x97,0x8d,0x8e,0x0b,0x0c,0x0d,0x0e,0x0f,
    0x10,0x11,0x12,0x13,0x9d,0x85,0x08,0x87,0x18,0x19,0x92,0x8f,0x1c,0x1d,0x1e,0x1f,
    0x80,0x81,0x82,0x83,0x84,0x0a,0x17,0x1b,0x88,0x89,0x8a,0x8b,0x8c,0x05,0x06,0x07,
    0x90,0x91,0x16,0x93,0x94,0x95,0x96,0x04,0x98,0x99,0x9a,0x9b,0x14,0x15,0x9e,0x1a,
    0x20,0xa0,0xe2,0xe4,0xe0,0xe1,0xe3,0x7d,0xe7,0xf1,0x23,0x2e,0x3c,0x28,0x2b,0x21,
    0x26,0xe9,0xea,0xeb,0xe8,0xed,0xee,0xef,0xec,0xdf,0xa4,0xc5,0x2a,0x29,0x3b,0x5e,
    0x2d,0x2f,0xc2,0xc4,0xc0,0xc1,0xc3,0x24,0xc7,0xd1,0xf8,0x2c,0x25,0x5f,0x3e,0x3f,
    0xa6,0xc9,0xca,0xcb,0xc8,0xcd,0xce,0xcf,0xcc,0x60,0x3a,0xc6,0xd8,0x27,0x3d,0x22,
    0x40,0x61,0x62,0x63,0x64,0x65,0x66,0x67,0x68,0x69,0xab,0xbb,0xf0,0xfd,0xfe,0xb1,
    0xb0,0x6a,0x6b,0x6c,0x6d,0x6e,0x6f,0x70,0x71,0x72,0xaa,0xba,0x7b,0xb8,0x5b,0x5d,
    0xb5,0xfc,0x73,0x74,0x75,0x76,0x77,0x78,0x79,0x7a,0xa1,0xbf,0xd0,0xdd,0xde,0xae,
    0xa2,0xa3,0xa5,0xb7,0xa9,0xa7,0xb6,0xbc,0xbd,0xbe,0xac,0x7c,0xaf,0xa8,0xb4,0xd7,
    0xe6,0x41,0x42,0x43,0x44,0x45,0x46,0x47,0x48,0x49,0xad,0xf4,0xf6,0xf2,0xf3,0xf5,
    0xe5,0x4a,0x4b,0x4c,0x4d,0x4e,0x4f,0x50,0x51,0x52,0xb9,0xfb,0x7e,0xf9,0xfa,0xff,
    0x5c,0xf7,0x53,0x54,0x55,0x56,0x57,0x58,0x59,0x5a,0xb2,0xd4,0xd6,0xd2,0xd3,0xd5,
    0x30,0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,0x39,0xb3,0xdb,0xdc,0xd9,0xda,0x9f,
};

void fast_e2a(char* src, size_t src_len) {
    for(size_t i = 0; i < src_len; ++i) {
        src[i] = e2a_table[(unsigned char) src[i]];
    }
}