Re: [PATCH] libgloss: arm: Add hardfault handler for M-profile

On 6/22/26 12:48, Richard Earnshaw wrote:
> On 12/06/2026 16:53, Christophe Lyon wrote:
>> After reaching a hardfault, the simulator enters an infinite loop
>> unless we map the handler to 'abort'.
>>
>> The patch adds this minimal setup for M-profile in
>> libgloss/arm/cpu-init/rdimon-aem.S and introduces the new
>> libgloss/arm/elf-mprofile-mps2.specs to add the mapping to the right
>> memory address.
>>
>> 2026-05-29  Andre Vieira <[email protected]>
>>     Christophe Lyon  <[email protected]>
>>
>>     libgloss/
>>     * Makefile.in: Add entry for arm/mprofile-mps2.specs.
>>     * arm/Makefile.inc: Add entry for mprofile-mps2.specs.
>>     * arm/cpu-init/rdimon-aem.S: Update comment. Add hardfault
>>     handler.
>>     * arm/elf-mprofile-mps2.specs: New file.
>> ---
>>   libgloss/Makefile.in                 |  1 +
>>   libgloss/arm/Makefile.inc            |  3 ++-
>>   libgloss/arm/cpu-init/rdimon-aem.S   | 11 +++++++++--
>>   libgloss/arm/elf-mprofile-mps2.specs | 26 ++++++++++++++++++++++++++
>>   4 files changed, 38 insertions(+), 3 deletions(-)
>>   create mode 100644 libgloss/arm/elf-mprofile-mps2.specs
>>
>> diff --git a/libgloss/Makefile.in b/libgloss/Makefile.in
>> index 5146a7880..c03ea4e6b 100644
>> --- a/libgloss/Makefile.in
>> +++ b/libgloss/Makefile.in
>> @@ -2255,6 +2255,7 @@ TEXINFO_TEX = ../texinfo/texinfo.tex
>>   @CONFIG_ARM_TRUE@    arm/aprofile-validation-v2m.specs \
>>   @CONFIG_ARM_TRUE@    arm/aprofile-ve-v2m.specs \
>>   @CONFIG_ARM_TRUE@    arm/aprofile-ve.specs arm/pid.specs \
>> +@CONFIG_ARM_TRUE@       arm/mprofile-mps2.specs \
>>   @CONFIG_ARM_TRUE@    arm/iq80310.specs
>>   @CONFIG_ARM_TRUE@arm_libgloss_linux_a_SOURCES = \
>>   @CONFIG_ARM_TRUE@    arm/linux-syscalls0.c \
>> diff --git a/libgloss/arm/Makefile.inc b/libgloss/arm/Makefile.inc
>> index 41fce3c99..5c740edcb 100644
>> --- a/libgloss/arm/Makefile.inc
>> +++ b/libgloss/arm/Makefile.inc
>> @@ -47,7 +47,8 @@ multilibtool_LIBRARIES += %D%/librdpmon.a
>>       %D%/aprofile-validation.specs \
>>       %D%/aprofile-validation-v2m.specs \
>>       %D%/aprofile-ve-v2m.specs \
>> -    %D%/aprofile-ve.specs
>> +    %D%/aprofile-ve.specs \
>> +    %D%/mprofile-mps2.specs
>>   multilibtool_DATA += \
>>       %D%/rdimon-crt0.o \
>>       %D%/rdimon-crt0-v2m.o
>> diff --git a/libgloss/arm/cpu-init/rdimon-aem.S b/libgloss/arm/cpu- 
>> init/rdimon-aem.S
>> index 2aacbeba9..c960924d4 100644
>> --- a/libgloss/arm/cpu-init/rdimon-aem.S
>> +++ b/libgloss/arm/cpu-init/rdimon-aem.S
> It looks to me as though there's no shared code in this file compared to 
> the a-profile variant, which makes me think that perhaps they should 
> just be separate files, rather than munged together when there's no 
> commonality beyond 'this is startup code'.
 > > Personally, I think it would be better to rename the existing file as
> something like rdimon-aem-a.S and then add a new one (say, rdimon-aem- 
> m.S) for the m-profile code.
> 
Indeed, before this patch the code is specific to A-profile, and this 
patch adds a section dedicated to M-profile (no nothing common with 
A-profile).
I think having 2 files makes sense but seems tricky to handle at 
Makefile level (wrt multilibs).
So maybe:
- rename rdi-mon-aem.S into rdimon-aem-a.S, and re-create rdi-mon-aem.S 
which only includes rdimon-aem-a.S
- add rdimon-aem-m.S and make rdi-mon-aem.S include it unconditionally

This way we have 2 separate source files, but no change to the build 
system and multilib support


>> @@ -25,7 +25,9 @@
>>   /* This file gives a basic initialisation of a Cortex-A series 
>> core.  It is
>>      the bare minimum required to get Cortex-A core running with a 
>> semihosting
>> -   interface.
>> +   interface.  For M-profile we only define a hardfault handler, 
>> required to
>> +   prevent the simulator from entering into an infinite loop.  The 
>> comments
>> +   below apply to A-profile only.
> 
> If I've missed something and this code does belong in this file, then 
> this whole comment needs properly restructuring.  There should be a 
> single top-level comment that just says something like "Provide the 
> basic CPU initialization for Armv7 and later CPUs.  We currently support 
> A-profile and M-profile.  Then the profile-specific details should be 
> moved inside the relevant ifdef sections.  It would be good to get rid 
> of the reference to 'Cortex-A' here as well (replace it with A-profile) 
> as there's nothing here that is specific to Arm's Cortex-* products: 
> this is defined by the architecture.

If I move rdimon-aem.S into rdimon-aem-a.S, I can probably make some 
small adjustments to this comment (and not add mentions of M-profile). 
This comment has been unmodified since ... 2013!
> 
> Finally, if you're keeping this in one place, the copyright dates at the 
> top of the file need updating.
> 
>>      It sets up a basic 1:1 phsyical address to virtual address mapping;
>>      turns the MMU on; enables branch prediction; activates any 
>> integrated
>> @@ -539,4 +541,9 @@ is_a15_a7:
>>   page_tables:
>>        PT7(0x1c0e)
>> -#endif //#if defined(__ARM_ARCH_7A__) || __ARM_ARCH_PROFILE == 'A'
>> +#elif  (__ARM_ARCH_PROFILE == 'M')
>> +    /* On M-profile, call abort in case of hardfault: this causes the 
>> simulator to
>> +       abort execution instead of going into an infinite loop.  */
>> +    .section .hardfault_handler_addr, "a"
>> +    .word abort
>> +#endif //#if defined(__ARM_ARCH_7A__) || (__ARM_ARCH_PROFILE == 'A')
>> diff --git a/libgloss/arm/elf-mprofile-mps2.specs b/libgloss/arm/elf- 
>> mprofile-mps2.specs
>> new file mode 100644
>> index 000000000..edaf71917
>> --- /dev/null
>> +++ b/libgloss/arm/elf-mprofile-mps2.specs
>> @@ -0,0 +1,26 @@
>> +# rdimon.specs
>> +#
>> +# Spec file for AArch32 M profile baremetal newlib with version 2 of
>> +# the AngelAPI semi-hosting using the SVC trap instruction.
>> +#
>> +# This version supports extensibility through an extension mechanism.
>> +
>> +%rename link_gcc_c_sequence                rdimon_link_gcc_c_sequence
>> +
>> +%rename link old_link
>> +
>> +*link:
>> +--section-start=.hardfault_handler_addr=0xc %(old_link)
>> +
>> +*rdimon_libc:
>> +%{!specs=nano.specs:-lc} %{specs=nano.specs:-lc_nano}
>> +
>> +*rdimon_libgloss:
>> +%{!specs=nano.specs:-lrdimon} %{specs=nano.specs:-lrdimon_nano}
>> +
>> +*link_gcc_c_sequence:
>> +%(rdimon_link_gcc_c_sequence) --start-group %G %(rdimon_libc) 
>> %(rdimon_libgloss) --end-group
>> +
>> +*startfile:
>> +crti%O%s crtbegin%O%s cpu-init/rdimon-aem.o%s %{!pg:rdimon-crt0%O%s} 
>> %{pg:rdimon-crt0%O%s}
>> +
>