Re: [ARM/FDPIC v5 01/21] [ARM] FDPIC: Add -mfdpic option support

[Christophe Lyon <christophe dot lyon at st dot com>]

On 16/07/2019 12:11, Richard Sandiford wrote:
> [This isn't really something that should be reviewed under global
> reviewership, but if it's either that or nothing, I'll do it anyway...]
>
> Christophe Lyon <christophe.lyon@st.com> writes:
> > 2019-XX-XX  Christophe Lyon  <christophe.lyon@st.com>
> > 	Mickaël Guêné  <mickael.guene@st.com>
> >
> > 	gcc/
> > 	* config/arm/arm.opt: Add -mfdpic option.
> > 	* doc/invoke.texi: Add documentation for -mfdpic.
> >
> > Change-Id: I0eabd1d11c9406fd4a43c4333689ebebbfcc4fe8
> >
> > diff --git a/gcc/config/arm/arm.opt b/gcc/config/arm/arm.opt
> > index 9067d49..2ed3bd5 100644
> > --- a/gcc/config/arm/arm.opt
> > +++ b/gcc/config/arm/arm.opt
> > @@ -306,3 +306,7 @@ Cost to assume for a branch insn.
> >   mgeneral-regs-only
> >   Target Report RejectNegative Mask(GENERAL_REGS_ONLY) Save
> >   Generate code which uses the core registers only (r0-r14).
> > +
> > +mfdpic
> > +Target Report Mask(FDPIC)
> > +Enable Function Descriptor PIC mode.
> > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> > index 29585cf..805d7cc 100644
> > --- a/gcc/doc/invoke.texi
> > +++ b/gcc/doc/invoke.texi
> > @@ -703,7 +703,8 @@ Objective-C and Objective-C++ Dialects}.
> >   -mrestrict-it @gol
> >   -mverbose-cost-dump @gol
> >   -mpure-code @gol
> > --mcmse}
> > +-mcmse @gol
> > +-mfdpic}
> >   
> >   @emph{AVR Options}
> >   @gccoptlist{-mmcu=@var{mcu}  -mabsdata  -maccumulate-args @gol
> > @@ -17912,6 +17913,23 @@ MOVT instruction.
> >   Generate secure code as per the "ARMv8-M Security Extensions: Requirements on
> >   Development Tools Engineering Specification", which can be found on
> >   @url{http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/ECM0359818_armv8m_security_extensions_reqs_on_dev_tools_1_0.pdf}.
> > +
> > +@item -mfdpic
> > +@itemx -mno-fdpic
> > +@opindex mfdpic
> > +@opindex mno-fdpic
> > +Select the FDPIC ABI, which uses function descriptors to represent
>
> Maybe "64-bit function descriptors"?  Just a suggestion, might not be useful.
>
> OK with that change, thanks.

OK, here is a new version, where I added a few words to explain that -static
is not supported.

Thanks,
Christophe

> Richard
>
> > +pointers to functions.  When the compiler is configured for
> > +@code{arm-*-uclinuxfdpiceabi} targets, this option is on by default
> > +and implies @option{-fPIE} if none of the PIC/PIE-related options is
> > +provided.  On other targets, it only enables the FDPIC-specific code
> > +generation features, and the user should explicitly provide the
> > +PIC/PIE-related options as needed.
> > +
> > +The opposite @option{-mno-fdpic} option is useful (and required) to
> > +build the Linux kernel using the same (@code{arm-*-uclinuxfdpiceabi})
> > +toolchain as the one used to build the userland programs.
> > +
> >   @end table
> >   
> >   @node AVR Options
> .

>From c936684e2b77ff5716bd8b67c617dcad088c72e0 Mon Sep 17 00:00:00 2001
From: Christophe Lyon <christophe.lyon@linaro.org>
Date: Thu, 8 Feb 2018 10:44:32 +0100
Subject: [ARM/FDPIC v6 01/24] [ARM] FDPIC: Add -mfdpic option support
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

2019-XX-XX  Christophe Lyon  <christophe.lyon@st.com>
	Mickaël Guêné  <mickael.guene@st.com>

	gcc/
	* config/arm/arm.opt: Add -mfdpic option.
	* doc/invoke.texi: Add documentation for -mfdpic.

Change-Id: I05b98d6ae87c2b3fc04dd7fba415c730accdf33e

diff --git a/gcc/config/arm/arm.opt b/gcc/config/arm/arm.opt
index 9067d49..2ed3bd5 100644
--- a/gcc/config/arm/arm.opt
+++ b/gcc/config/arm/arm.opt
@@ -306,3 +306,7 @@ Cost to assume for a branch insn.
 mgeneral-regs-only
 Target Report RejectNegative Mask(GENERAL_REGS_ONLY) Save
 Generate code which uses the core registers only (r0-r14).
+
+mfdpic
+Target Report Mask(FDPIC)
+Enable Function Descriptor PIC mode.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 29585cf..b77fa06 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -703,7 +703,8 @@ Objective-C and Objective-C++ Dialects}.
 -mrestrict-it @gol
 -mverbose-cost-dump @gol
 -mpure-code @gol
--mcmse}
+-mcmse @gol
+-mfdpic}
 
 @emph{AVR Options}
 @gccoptlist{-mmcu=@var{mcu}  -mabsdata  -maccumulate-args @gol
@@ -17912,6 +17913,27 @@ MOVT instruction.
 Generate secure code as per the "ARMv8-M Security Extensions: Requirements on
 Development Tools Engineering Specification", which can be found on
 @url{http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/ECM0359818_armv8m_security_extensions_reqs_on_dev_tools_1_0.pdf}.
+
+@item -mfdpic
+@itemx -mno-fdpic
+@opindex mfdpic
+@opindex mno-fdpic
+Select the FDPIC ABI, which uses 64-bit function descriptors to
+represent pointers to functions.  When the compiler is configured for
+@code{arm-*-uclinuxfdpiceabi} targets, this option is on by default
+and implies @option{-fPIE} if none of the PIC/PIE-related options is
+provided.  On other targets, it only enables the FDPIC-specific code
+generation features, and the user should explicitly provide the
+PIC/PIE-related options as needed.
+
+Note that static linking is not supported because it would still
+involve the dynamic linker when the program self-relocates.  If such
+behaviour is acceptable, use -static and -Wl,-dynamic-linker options.
+
+The opposite @option{-mno-fdpic} option is useful (and required) to
+build the Linux kernel using the same (@code{arm-*-uclinuxfdpiceabi})
+toolchain as the one used to build the userland programs.
+
 @end table
 
 @node AVR Options
-- 
2.6.3