AM6442: Query regarding #pragma pack in TI ARM compiler

Rahul Prabhu

Part Number: AM6442

Posting this on behalf of a customer:

ARM Optimizing C / C ++ Compiler v20.2.0.LTS User's Guide "5.11.24 The pack Pragma" was referred to and defined as follows in R5F.
■Definition
・test.h
define XXX 16

#pragma pack (8)
typedef struct test_tg {
    Uint16 aaa;
    int16   bbb;
    float32 ccc;
    float32 ddd[XXX];
    int16   eee;
    int16   fff;
} TEST_PACK;
#pragma pack ()

・test.c
volatile TEST_PACK test __attribute__((section("TEST_SECTION")));

The build passes with this definition (no error, no warning), but when I check the map file, it seems that it is not aligned with 8 bytes.
I think there are settings that are required in addition to the definition?

■map file
70080088 test <-The size is 0x4C (76). The #pragma pack, assumed to be 0x50 (80)
700800d4 dmy0

over 4 years ago

0 George Mock over 4 years ago

TI__Guru**** 249760 points

Just for the moment, please ignore #pragma pack. What problem do you want to solve? What are all the properties you want the structure test to have?

Thanks and regards,

-George

0 Rahul Prabhu over 4 years ago

TI__Guru** 116170 points

The intent is to always align the struct with typedef TEST_PACK ( Example: test) address to align at 8 bytes boundary. The intent is to minimize the impact of cache when reading data from these structs. Should the pragma be used with all struct where they are defined instead of around the typdef ?

0 George Mock over 4 years ago in reply to Rahul Prabhu

TI__Guru**** 249760 points

Do not use #pragma pack. Apply the aligned attribute to the typedef ...

typedef struct test_tg {
    Uint16  aaa;
    int16   bbb;
    float32 ccc;
    float32 ddd[XXX];
    int16   eee;
    int16   fff;
} TEST_PACK __attribute__((aligned(8)));

Thanks and regards,

-George

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AM6442: Query regarding #pragma pack in TI ARM compiler