https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106873
Bug ID: 106873
Summary: unsigned short skips byte when used for memory mapping
depending on position in structure
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: info at kemalakcam dot com
Target Milestone: ---
Please move to the correct component in reporting menu as this problem is not
necessarily c++
// ============================================================================
// File: ka_example_pointer.cpp
// Desc: Software programming example of pointers
// Date: 2020/12/25 Ali Kemal Akçam - ka_example_pointer.cpp created.
// ============================================================================
// source code shortened to report bug.
// memory mapping with unsigned short does not show intented result.
// both 'unsigned short' and 'unsigned short int' skips one byte depending on
position
// tested with
// gcc --version
// (Debian 4.9.2-10) 4.9.2
// (Debian 8.3.0-6) 8.3.0
// 12.1.0
// gcc version 4.9.2 compiled as
// gcc -lstdc++ -std=c++11 ka_example_pointer_very_brief.cpp -o
ka_example_pointer_very_brief.o
// gcc version 12.1.0 compiled as
// gcc -lstdc++ ka_example_pointer_very_brief.cpp -o
ka_example_pointer_very_brief.o
#include <stdio.h>
typedef struct
{
unsigned char a; // 1 byte
unsigned char b; // 1 byte
unsigned char c; // 1 byte
unsigned char d; // 1 byte
unsigned char e; // 1 byte
unsigned char f; // 1 byte
unsigned char g; // 1 byte
unsigned char h; // 1 byte
} tsMMP_bytes; // 8 bytes
typedef struct
{
unsigned char a; // 1 byte
unsigned short b; // 2 bytes - skips one byte here
unsigned char c; // 1 byte
unsigned char d; // 1 byte
unsigned short e; // 2 bytes - does not skip one byte here
unsigned char f; // 1 byte
} tsMMP_mixed; // 8 bytes
typedef struct
{
unsigned char a; // 1 byte
unsigned char b; // 1 byte
unsigned short c; // 2 bytes - does not skip one byte here
unsigned char d; // 1 byte
unsigned short e; // 2 bytes - skips one byte here
unsigned char f; // 1 byte
} tsMMP_mixed2; // 8 bytes
typedef struct
{
unsigned char a; // 1 byte
unsigned short b; // 2 bytes - skips one byte here
unsigned char c; // 1 byte
unsigned short d; // 2 bytes - skips one byte here
unsigned char e; // 1 byte
unsigned char f; // 1 byte
} tsMMP_mixed3; // 8 bytes
typedef struct
{
unsigned char l;
char h;
} tsWord; // signed word DOES NOT WORK!
typedef struct
{
unsigned char a; // 1 byte
tsWord b; // 2 bytes - works properly
unsigned char c; // 1 byte
unsigned char d; // 1 byte
tsWord e; // 2 bytes - works properly
unsigned char f; // 1 byte
} tsMMP_mixed_struct_word; // 8 bytes - correctly maps to another linear
memory
// 20201225T0311 : Kemal Akcam : Mixed typedef struct works perfectly while
using as memory stencil for memory mapping.
typedef struct
{
unsigned char a;
unsigned char b;
} tsShort;
typedef struct
{
unsigned char a; // 1 byte
tsShort b; // 2 bytes - works properly
unsigned char c; // 1 byte
unsigned char d; // 1 byte
tsShort e; // 2 bytes - works properly
unsigned char f; // 1 byte
} tsMMP_mixed_struct; // 8 bytes - correctly maps to another linear memory
class c
{
public:
c(){};
~c(){};
unsigned char m[16] = { 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
0x18, 0x19, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25 };
void printContent(void);
};
void c::printContent(void)
{
int i;
printf("Memory content ");
for(i=0; i<16; i++) printf("%X ", m[i]);
printf("\n");
printf("tsMMP_bytes ");
tsMMP_bytes *pB;
pB = (tsMMP_bytes *)&m;
printf("%X %X %X %X %X %X %X %X ",
pB->a,
pB->b,
pB->c,
pB->d,
pB->e,
pB->f,
pB->g,
pB->h);
printf("\n");
{
printf("tsMMP_mixed ");
tsMMP_mixed *pM;
pM = (tsMMP_mixed *)&m;
printf("%X %X %X %X %X %X <--- 11 is NOT there",
pM->a,
pM->b,
pM->c,
pM->d,
pM->e,
pM->f);
printf("\n");
}
{
printf("tsMMP_mixed2 ");
tsMMP_mixed2 *pM;
pM = (tsMMP_mixed2 *)&m;
printf("%X %X %X %X %X %X <--- 15 is NOT there",
pM->a,
pM->b,
pM->c,
pM->d,
pM->e,
pM->f);
printf("\n");
}
{
printf("tsMMP_mixed3 ");
tsMMP_mixed3 *pM;
pM = (tsMMP_mixed3 *)&m;
printf("%X %X %X %X %X %X <--- 11 and 15 is NOT there",
pM->a,
pM->b,
pM->c,
pM->d,
pM->e,
pM->f);
printf("\n");
}
printf("tsMMP_mixed_struct ");
tsMMP_mixed_struct *pMS;
pMS = (tsMMP_mixed_struct *)&m;
printf("%X %X %X %X %X %X <--- 11 and 15 is there",
pMS->a,
pMS->b,
pMS->c,
pMS->d,
pMS->e,
pMS->f);
printf("\n");
printf("tsMMP_mixed_struct_word ");
tsMMP_mixed_struct_word *pMWord;
pMWord = (tsMMP_mixed_struct_word *)&m;
printf("%X %X %X %X %X %X <--- 11 and 15 is there",
pMWord->a,
pMWord->b,
pMWord->c,
pMWord->d,
pMWord->e,
pMWord->f);
printf("\n");
printf("tsMMP_mixed_struct_word ");
short int *b = (short int *)&(pMWord->b);
short int *e = (short int *)&(pMWord->e);
printf(" corr b e %04X %04X ", *b, *e);
printf("\n");
printf("tsMMP_mixed_struct_word ");
printf("%X %X %X %X %X %X %X %X ",
pMWord->a,
pMWord->b.h,
pMWord->b.l,
pMWord->c,
pMWord->d,
pMWord->e.h,
pMWord->e.l,
pMWord->f);
printf("\n");
}
int main(int argc, char **argv)
{
c *n = new c();
n->printContent();
n->~c();
return 0;
}
/*
Output:
ka@localhost:~/projects/ka_projects/pointer_test$ gcc -lstdc++
ka_example_pointer_very_brief.cpp -o ka_example_pointer_very_brief.o
ka@localhost:~/projects/ka_projects/pointer_test$
./ka_example_pointer_very_brief.o
Memory content 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
tsMMP_bytes 10 11 12 13 14 15 16 17
tsMMP_mixed 10 1312 14 15 1716 18 <--- 11 is NOT there
tsMMP_mixed2 10 11 1312 14 1716 18 <--- 15 is NOT there
tsMMP_mixed3 10 1312 14 1716 18 19 <--- 11 and 15 is NOT there
tsMMP_mixed_struct 10 1211 13 14 1615 17 <--- 11 and 15 is there
tsMMP_mixed_struct_word 10 1211 13 14 1615 17 <--- 11 and 15 is there
tsMMP_mixed_struct_word corr b e 1211 1615
tsMMP_mixed_struct_word 10 12 11 13 14 16 15 17
*/
