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From: Alexander Lakhin <[email protected]>
To: Greg Burd <[email protected]>
To: Tom Lane <[email protected]>
To: Michael Paquier <[email protected]>
Cc: pgsql-hackers <[email protected]>
Cc: Thomas Munro <[email protected]>
Subject: Re: pgcrypto/des tests fail on riscv64 due to clang's code generation anomaly
Date: Mon, 16 Mar 2026 20:00:00 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>

Hello,

16.03.2026 14:13, Greg Burd wrote:
>> Seems like this might be worth a bug report to the clang people.
> Thanks Alexander for digging and a solid report of the issue, and Michael for spending some time on this, and Tom for chiming in as well.  I agree this looks like a compiler issue.  I know that Thomas (added/CC'ed) you've posted bugs against clang before, any thoughts on this one?
>

Please find attached the reduced test code, which works for me as follows:
$ clang-20 -O2 -march=rv64gcv crypt-des-test.c -o crypt-des-test && ./crypt-des-test
!!!des_init| un_pbox: 15 6 19 20 28 11 27 16 0 14 22 25 4 17 30 9 1 7 23 13 31 26 2 8 18 12 29 5 21 10 3 24

$ clang-20 -O2 -march=rv64gc crypt-des-test.c -o crypt-des-test && ./crypt-des-test
!!!des_init| un_pbox: 8 16 22 30 12 27 1 17 23 15 29 5 25 19 9 0 7 13 24 2 3 28 10 18 31 11 21 6 4 26 14 20

$ clang-20 -O1 -march=rv64gcv crypt-des-test.c -o crypt-des-test && ./crypt-des-test
!!!des_init| un_pbox: 8 16 22 30 12 27 1 17 23 15 29 5 25 19 9 0 7 13 24 2 3 28 10 18 31 11 21 6 4 26 14 20

$ clang-20 --version
Ubuntu clang version 20.1.2 (0ubuntu1~24.04.2)

Best regards,
Alexander

Attachments:

  [text/x-csrc] crypt-des-test.c (741B, 2-crypt-des-test.c)
  download | inline:
#include <stdio.h>

#define uint8 unsigned char
#define uint32 unsigned int

#define pg_compiler_barrier()      __asm__ __volatile__("" ::: "memory")

static uint8 un_pbox[32];
static uint8 pbox[32] = {
	16, 7, 20, 21, 29, 12, 28, 17, 1, 15, 23, 26, 5, 18, 31, 10,
	2, 8, 24, 14, 32, 27, 3, 9, 19, 13, 30, 6, 22, 11, 4, 25
};

static void
des_init(void)
{
	int		i;
	/*
	 * Invert the P-box permutation, and convert into OR-masks for handling
	 * the output of the S-box arrays setup above.
	 */
	for (i = 0; i < 32; i++)
{

		un_pbox[pbox[i] - 1] = i;
//pg_compiler_barrier();
}

fprintf(stderr, "!!!des_init| un_pbox:");
	for (i = 0; i < 32; i++)
		fprintf(stderr, " %d", un_pbox[i]);
fprintf(stderr, "\n");

}

int main()
{
	des_init();
}

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