Re: [PATCH] kexec-tools: Fix conversion overflow when compiling on 32-bit platforms

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On 03.10.19 10:14, Simon Horman wrote:
On Tue, Oct 01, 2019 at 05:14:16PM +0200, Helge Deller wrote:
When compiling kexec-tools on a 32-bit platform, assigning an
(unsigned long long) value to an (unsigned long) variable creates
this warning:

elf_info.c: In function 'read_phys_offset_elf_kcore':
elf_info.c:805:14: warning: conversion from 'long long unsigned int' to 'long unsigned int' changes value from '18446744073709551615' to '4294967295'
   805 |  *phys_off = UINT64_MAX;
       |              ^~~~~~~~~~

Fix it by casting UINT64_MAX to (unsigned long) before storing it to *phys_off.

Signed-off-by: Helge Deller <deller@xxxxxx>

diff --git a/util_lib/elf_info.c b/util_lib/elf_info.c
index 2bce5cb..4d16983 100644
--- a/util_lib/elf_info.c
+++ b/util_lib/elf_info.c
@@ -802,7 +802,7 @@ int read_phys_offset_elf_kcore(int fd, unsigned long *phys_off)
  {
  	int ret;

-	*phys_off = UINT64_MAX;
+	*phys_off = (unsigned long) UINT64_MAX;

This seems to mask the problem that UINT64_MAX is not the right
initialiser for unsigned long values on 32-bit platforms.
Could we consider using UINT64_MAX from limits.h instead?

UINT64 means it is a 64bit value, while "unsigned long" is either 32-bit,
64bit (or maybe in the future even 128bit?).
Even assigning UINT32_MAX on a 32bit platform might be wrong.
So I think the cast above is probably the best solution.

Helge

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