3rd-party/linux-kernel-module-cheat
1
0
Fork 0
mirror of https://github.com/cirosantilli/linux-kernel-module-cheat.git synced 2026-01-25 11:11:35 +01:00
Code Issues Releases Wiki Activity

asm: more links

Browse Source
This commit is contained in:
Ciro Santilli 六四事件 法轮功
2019-05-05 00:00:00 +00:00
parent 549bd4a7fd
commit 3388d72bb2
25 changed files with 154 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files

109
README.adoc
View File

@@ -11380,6 +11380,11 @@ TODO
Notice how we give the actual assembly line number where the failing assert was!
Other setup sanity checks that you might want to look into include:
* link:userland/arch/empty.S[]
* link:userland/arch/fail.S[]
=== User vs system assembly
By "userland assembly", we mean "the parts of the ISA which can be freely used from userland".
@@ -11388,12 +11393,82 @@ Most ISAs are divided into a system and userland part, and to running the system
One big difference between both is that we can run userland assembly on <<userland-setup>>, which is easier to get running and debug.
In particular, all the examples outside of <<linux-system-calls,freestanding directories>> link to the C standard library for IO, which is very convenient and portable across host OSes.
In particular, most userland assembly examples link to the C standard library: <<userland-assembly-c-standard-library>>.
Userland assembly is generally simpler, and a pre-requisite for <<baremetal-setup>>.
System-land assembly cheats will be put under: <<baremetal-setup>>.
=== Userland assembly C standard library
All examples outside of <<linux-system-calls,freestanding directories>> link to the C standard library.
This allows using the C standard library for IO, which is very convenient and portable across host OSes.
It also exposes other non-IO functionality that is very convenient such as `memcmp`.
The C standard library infrastructure is implemented in the following files:
* link:userland/arch/main.c[]
* link:userland/arch/common.h[]
* link:userland/arch/x86_64/common_arch.h[]
* link:userland/arch/arm/common_arch.h[]
* link:userland/arch/aarch64/common_arch.h[]
=== Inline assembly
Examples under `arch/<arch>/c/` directories show to how use inline assembly from higher level languages such as C:
* x86_64
** link:userland/arch/x86_64/c/inc.c[]
** link:userland/arch/x86_64/c/add.c[]
* arm
** link:userland/arch/arm/c/inc.c[]
** link:userland/arch/arm/c/inc_memory.c[]
** link:userland/arch/arm/c/inc_memory_global.c[]
** link:userland/arch/arm/c/add.c[]
* aarch64
** link:userland/arch/aarch64/c/earlyclobber.c[]
** link:userland/arch/aarch64/c/inc.c[]
** link:userland/arch/aarch64/c/multiline.cpp[]
==== Inline assembly register variables
Used notably in some of the <<linux-system-calls>> setups:
* link:userland/arch/arm/reg_var.c[]
* link:userland/arch/aarch64/reg_var.c[]
* link:userland/arch/aarch64/reg_var_float.c[]
In x86, makes it possible to access variables not exposed with the one letter register constraints.
In arm, it is the only way to achieve this effect: https://stackoverflow.com/questions/10831792/how-to-use-specific-register-in-arm-inline-assembler
==== Inline assembly scratch registers
How to use temporary registers in inline assembly:
* x86_64
** link:userland/arch/x86_64/c/scratch.c[]
** link:userland/arch/x86_64/c/scratch_hardcode.c[]
Bibliography: https://stackoverflow.com/questions/6682733/gcc-prohibit-use-of-some-registers/54963829#54963829
==== Inline assembly early-clobbers
An example of using the `&` early-clobber modifier: link:userland/arch/aarch64/earlyclobber.c
More details at: https://stackoverflow.com/questions/15819794/when-to-use-earlyclobber-constraint-in-extended-gcc-inline-assembly/54853663#54853663
The assertion may fail without it. It actually does fail in GCC 8.2.0.
==== Inline assembly floating point ARM
Not documented as of GCC 8.2, but possible: https://stackoverflow.com/questions/53960240/armv8-floating-point-output-inline-assembly
* link:userland/arch/arm/c/inc_float.c[]
* link:userland/arch/aarch64/c/inc_float.c[]
=== Linux system calls
The following <<userland-setup>> programs illustrate how to make system calls:
@@ -11436,11 +11511,35 @@ Determining the ARM syscall interface:
Questions about the C inline assembly examples:
* x86_64: https://stackoverflow.com/questions/9506353/how-to-invoke-a-system-call-via-sysenter-in-inline-assembly/54956854#54956854
* ARM: https://stackoverflow.com/questions/21729497/doing-a-syscall-without-libc-using-arm-inline-assembly
=== Calling conventions
* x86_64
** https://stackoverflow.com/questions/9506353/how-to-invoke-a-system-call-via-sysenter-in-inline-assembly/54956854#54956854
* ARM
** https://stackoverflow.com/questions/10831792/how-to-use-specific-register-in-arm-inline-assembler
** https://stackoverflow.com/questions/21729497/doing-a-syscall-without-libc-using-arm-inline-assembly
** link:userland/arch/x86_64/common_arch.h[] `ENTRY` and `EXIT`
==== ARM calling convention
Call C standard library functions from assembly and vice versa.
* arm
** link:userland/arch/arm/common_arch.h[] `ENTRY` and `EXIT`
** link:userland/arch/arm/c_from_asm.S[]
* aarch64
** link:userland/arch/aarch64/common_arch.h[] `ENTRY` and `EXIT`
** link:userland/arch/aarch64/c/asm_from_c.c[]
ARM Architecture Procedure Call Standard (AAPCS) is the name that ARM Holdings gives to the calling convention.
Official specification: http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042f/IHI0042F_aapcs.pdf
Bibliography:
* https://en.wikipedia.org/wiki/Calling_convention#ARM_(A32) Wiki contains the master list as usual.
* http://stackoverflow.com/questions/8422287/calling-c-functions-from-arm-assembly
* http://stackoverflow.com/questions/261419/arm-to-c-calling-convention-registers-to-save
* https://stackoverflow.com/questions/10494848/arm-whats-the-difference-between-apcs-and-aapcs-abi
== x86 userland assembly