diff options
author | Alexander Fedotov <alfedotov@gmail.com> | 2019-07-22 19:18:53 +0300 |
---|---|---|
committer | Corinna Vinschen <corinna@vinschen.de> | 2019-07-23 11:00:06 +0300 |
commit | 942f60d714e18cd775dc8b0a661cf70eef162bcc (patch) | |
tree | 022f11cff9037a26af8acde75b3b54f9a5143f8c /libgloss | |
parent | ae59d0930803abf0b2228999d4cdff08679b62cd (diff) |
Stack Pointer and Stack Limit initialization refactored.
SP initialization changes:
1. set default value in semihosting case as well
2. moved existing SP & SL init code for processor modes in separate routine and made it as "hook"
3. init SP for processor modes in Thumb mode as well
Add new macro FN_RETURN, FN_EH_START and FN_EH_END.
Diffstat (limited to 'libgloss')
-rw-r--r-- | libgloss/arm/arm.h | 26 | ||||
-rw-r--r-- | libgloss/arm/crt0.S | 290 |
2 files changed, 227 insertions, 89 deletions
diff --git a/libgloss/arm/arm.h b/libgloss/arm/arm.h index 0489f2d92..10e5b0509 100644 --- a/libgloss/arm/arm.h +++ b/libgloss/arm/arm.h @@ -61,4 +61,30 @@ # define HAVE_CALL_INDIRECT #endif +/* A and R profiles (and legacy Arm). + Current Program Status Register (CPSR) + M[4:0] Mode bits. M[4] is always 1 for 32-bit modes. + T[5] 1: Thumb, 0: ARM instruction set + F[6] 1: disables FIQ + I[7] 1: disables IRQ + A[8] 1: disables imprecise aborts + E[9] 0: Little-endian, 1: Big-endian + J[24] 1: Jazelle instruction set + */ +#define CPSR_M_USR 0x00 /* User mode. */ +#define CPSR_M_FIQ 0x01 /* Fast Interrupt mode. */ +#define CPSR_M_IRQ 0x02 /* Interrupt mode. */ +#define CPSR_M_SVR 0x03 /* Supervisor mode. */ +#define CPSR_M_MON 0x06 /* Monitor mode. */ +#define CPSR_M_ABT 0x07 /* Abort mode. */ +#define CPSR_M_HYP 0x0A /* Hypervisor mode. */ +#define CPSR_M_UND 0x0B /* Undefined mode. */ +#define CPSR_M_SYS 0x0F /* System mode. */ +#define CPSR_M_32BIT 0x10 /* 32-bit mode. */ +#define CPSR_T_BIT 0x20 /* Thumb bit. */ +#define CPSR_F_MASK 0x40 /* FIQ bit. */ +#define CPSR_I_MASK 0x80 /* IRQ bit. */ + +#define CPSR_M_MASK 0x0F /* Mode mask except M[4]. */ + #endif /* _LIBGLOSS_ARM_H */ diff --git a/libgloss/arm/crt0.S b/libgloss/arm/crt0.S index 1deb73aa5..3e740c654 100644 --- a/libgloss/arm/crt0.S +++ b/libgloss/arm/crt0.S @@ -59,6 +59,21 @@ .endm #endif +/* Annotation for EABI unwinding tables. */ +.macro FN_EH_START +#if defined(__ELF__) && !defined(__USING_SJLJ_EXCEPTIONS__) + .fnstart +#endif +.endm + +.macro FN_EH_END +#if defined(__ELF__) && !defined(__USING_SJLJ_EXCEPTIONS__) + /* Protect against unhandled exceptions. */ + .cantunwind + .fnend +#endif +.endm + .macro indirect_call reg #ifdef HAVE_CALL_INDIRECT blx \reg @@ -68,16 +83,171 @@ #endif .endm +/* For armv4t and newer, toolchains will transparently convert + 'bx lr' to 'mov pc, lr' if needed. GCC has deprecated support + for anything older than armv4t, but this should handle that + corner case in case anyone needs it anyway. */ +.macro FN_RETURN +#if __ARM_ARCH <= 4 && __ARM_ARCH_ISA_THUMB == 0 + mov pc, lr +#else + bx lr +#endif +.endm + + + +/****************************************************************************** +* User mode only: This routine makes default target specific Stack +* +-----+ <- SL_sys, Pointer initialization for different processor modes: +* | | SL_usr FIQ, Abort, IRQ, Undefined, Supervisor, System (User) +* | SYS | and setups a default Stack Limit in-case the code has +* | USR | -=0x10000 been compiled with "-mapcs-stack-check" for FIQ and +* | | System (User) modes. +* | | +* +-----+ <- initial SP, +* becomes SP_sys Hard-wiring SL value is not ideal, since there is +* and SL_usr currently no support for checking that the heap and +* stack have not collided, or that this default 64k is +* All modes: is enough for the program being executed. However, +* +-----+ <- SL_sys, it ensures that this simple crt0 world will not +* | | SL_usr immediately cause an overflow event. +* | SYS | +* | USR | -=0x10000 We go through all execution modes and set up SP +* | | for each of them. +* +-----+ <- SP_sys, +* | | SP_usr Notes: +* | SVC | -= 0x8000 - This code will not work as intended if the system +* | | starts in secure mode. In particular the methods +* +-----+ <- SP_svc of getting in and out of secure state are not as +* | | simple as writing to the CPSR mode bits. +* | IRQ | -= 0x2000 - Mode switch via CPSR is not allowed once in +* | | non-privileged mode, so we take care not to enter +* ^ +-----+ <- SP_und "User" to set up its SP, and also skip most +* s | | operations if already in that mode. +* t | UND | -= 0x1000 +* a | | Input parameters: +* c +-----+ <- SP_und - sp - Initialized SP +* k | | - r2 - May contain SL value from semihosting +* | ABT | -= 0x1000 SYS_HEAPINFO call +* g | | Scratch registers: +* r +-----+ <- SP_abt, - r1 - new value of CPSR +* o | | SL_fiq - r2 - intermediate value (in standalone mode) +* w | FIQ | -= 0x1000 - r3 - new SP value +* t | | - r4 - save/restore CPSR on entry/exit +* h +-----+ <- initial SP, +* becomes SP_fiq Declared as "weak" so that user can write and use +* his own implementation if current doesn't fit. +* +******************************************************************************/ + .align 0 + FUNC_START _stack_init + .weak FUNCTION (_stack_init) + FN_EH_START + + /* M profile doesn't have CPSR register. */ +#if (__ARM_ARCH_PROFILE != 'M') + /* Following code is compatible for both ARM and Thumb ISA. */ + mrs r4, CPSR + /* Test mode bits - in User of all are 0. */ + tst r4, #(CPSR_M_MASK) + /* "eq" means r4 AND #0x0F is 0. */ + beq .Lskip_cpu_modes + + mov r3, sp /* Save input SP value. */ + + /* FIQ mode, interrupts disabled. */ + mov r1, #(CPSR_M_FIQ|CPSR_M_32BIT|CPSR_I_MASK|CPSR_F_MASK) + msr CPSR_c, r1 + mov sp, r3 + sub sl, sp, #0x1000 /* FIQ mode has its own SL. */ + + /* Abort mode, interrupts disabled. */ + mov r3, sl + mov r1, #(CPSR_M_ABT|CPSR_M_32BIT|CPSR_I_MASK|CPSR_F_MASK) + msr CPSR_c, r1 + mov sp, r3 + sub r3, r3, #0x1000 + + /* Undefined mode, interrupts disabled. */ + mov r1, #(CPSR_M_UND|CPSR_M_32BIT|CPSR_I_MASK|CPSR_F_MASK) + msr CPSR_c, r1 + mov sp, r3 + sub r3, r3, #0x1000 + + /* IRQ mode, interrupts disabled. */ + mov r1, #(CPSR_M_IRQ|CPSR_M_32BIT|CPSR_I_MASK|CPSR_F_MASK) + msr CPSR_c, r1 + mov sp, r3 + sub r3, r3, #0x2000 + + /* Supervisory mode, interrupts disabled. */ + mov r1, #(CPSR_M_SVR|CPSR_M_32BIT|CPSR_I_MASK|CPSR_F_MASK) + msr CPSR_c, r1 + mov sp, r3 + + sub r3, r3, #0x8000 /* Min size 32k. */ + bic r3, r3, #0x00FF /* Align with current 64k block. */ + bic r3, r3, #0xFF00 + +# if __ARM_ARCH >= 4 + /* System (shares regs with User) mode, interrupts disabled. */ + mov r1, #(CPSR_M_SYS|CPSR_M_32BIT|CPSR_I_MASK|CPSR_F_MASK) + msr CPSR_c, r1 + mov sp, r3 +# else + /* Keep this for ARMv3, but GCC actually dropped it. */ + /* Move value into user mode SP without changing modes, */ + /* via '^' form of ldm. */ + str r3, [r3, #-4] + ldmdb r3, {sp}^ +# endif + + /* Back to original mode, presumably SVC, with diabled FIQ/IRQ. */ + orr r4, r4, #(CPSR_I_MASK|CPSR_F_MASK) + msr CPSR_c, r4 + +.Lskip_cpu_modes: +#endif + + /* Set SL register. */ +#if defined (ARM_RDI_MONITOR) /* semihosting */ + cmp r2, #0 + beq .Lsl_forced_zero + /* Allow slop for stack overflow handling and small frames. */ +# ifdef THUMB1_ONLY + adds r2, #128 + adds r2, #128 + mov sl, r2 +# else + add sl, r2, #256 +# endif +.Lsl_forced_zero: + +#else /* standalone */ + /* r3 contains SP for System/User mode. Set SL = SP - 0x10000. */ + #ifdef THUMB1_ONLY + movs r2, #64 + lsls r2, r2, #10 + subs r2, r3, r2 + mov sl, r2 + #else + /* Still assumes 256bytes below SL. */ + sub sl, r3, #64 << 10 + #endif +#endif + + FN_RETURN + FN_EH_END + + /******************************************************************************* * Main library startup code. *******************************************************************************/ .align 0 FUNC_START _mainCRTStartup FUNC_START _start -#if defined(__ELF__) && !defined(__USING_SJLJ_EXCEPTIONS__) - /* Annotation for EABI unwinding tables. */ - .fnstart -#endif + FN_EH_START /* __ARM_ARCH_PROFILE is defined from GCC 4.8 onwards, however __ARM_ARCH_7A has been defined since 4.2 onwards, which is when v7-a support was added @@ -144,42 +314,33 @@ .LC32: ldr r1, [r0, #8] ldr r2, [r0, #12] - /* We skip setting sp/sl if 0 returned from semihosting. + /* We skip setting SP/SL if 0 returned from semihosting. - According to semihosting docs, if 0 returned from semihosting, the system was unable to calculate the real value, so it's ok - to skip setting sp/sl to 0 here. + to skip setting SP/SL to 0 here. - Considering M-profile processors, We might want to initialize - sp by the first entry of vector table and return 0 to SYS_HEAPINFO - semihosting call, which will be skipped here. */ + SP by the first entry of vector table and return 0 to SYS_HEAPINFO + semihosting call, which will be skipped here. + - Considering R-profile processors there is no automatic SP init by hardware + so we need to initialize it by default value. */ + ldr r3, .Lstack cmp r1, #0 beq .LC26 - mov sp, r1 + mov r3, r1 .LC26: - cmp r2, #0 - beq .LC27 + mov sp, r3 - /* Allow slop for stack overflow handling and small frames. */ -#ifdef THUMB1_ONLY - adds r2, #128 - adds r2, #128 - mov sl, r2 -#else - add sl, r2, #256 -#endif + /* r2 (SL value) will be used in _stack_init. */ + bl FUNCTION (_stack_init) -.LC27: -#else - /* Set up the stack pointer to a fixed value. */ + +#else /* standalone */ + /* Set up the stack pointer to a fixed value. */ /* Changes by toralf: - Allow linker script to provide stack via __stack symbol - see defintion of .Lstack - Provide "hooks" that may be used by the application to add - custom init code - see .Lhwinit and .Lswinit - - Go through all execution modes and set up stack for each of them. - Loosely based on init.s from ARM/Motorola example code. - Note: Mode switch via CPSR is not allowed once in non-privileged - mode, so we take care not to enter "User" to set up its sp, - and also skip most operations if already in that mode. */ + custom init code - see .Lhwinit and .Lswinit. */ ldr r3, .Lstack cmp r3, #0 @@ -194,61 +355,14 @@ ldreq r3, .LC0 #endif /* Note: This 'mov' is essential when starting in User, and ensures we - always get *some* sp value for the initial mode, even if we + always get *some* SP value for the initial mode, even if we have somehow missed it below (in which case it gets the same value as FIQ - not ideal, but better than nothing). */ mov sp, r3 -#ifdef PREFER_THUMB - /* XXX Fill in stack assignments for interrupt modes. */ -#else - mrs r2, CPSR - tst r2, #0x0F /* Test mode bits - in User of all are 0. */ - beq .LC23 /* "eq" means r2 AND #0x0F is 0. */ - msr CPSR_c, #0xD1 /* FIRQ mode, interrupts disabled. */ - mov sp, r3 - sub sl, sp, #0x1000 /* This mode also has its own sl (see below). */ - - mov r3, sl - msr CPSR_c, #0xD7 /* Abort mode, interrupts disabled. */ - mov sp, r3 - sub r3, r3, #0x1000 - - msr CPSR_c, #0xDB /* Undefined mode, interrupts disabled. */ - mov sp, r3 - sub r3, r3, #0x1000 - - msr CPSR_c, #0xD2 /* IRQ mode, interrupts disabled. */ - mov sp, r3 - sub r3, r3, #0x2000 - - msr CPSR_c, #0xD3 /* Supervisory mode, interrupts disabled. */ - mov sp, r3 - sub r3, r3, #0x8000 /* Min size 32k. */ - bic r3, r3, #0x00FF /* Align with current 64k block. */ - bic r3, r3, #0xFF00 + /* We don't care of r2 value in standalone. */ + bl FUNCTION (_stack_init) - str r3, [r3, #-4] /* Move value into user mode sp without */ - ldmdb r3, {sp}^ /* changing modes, via '^' form of ldm. */ - orr r2, r2, #0xC0 /* Back to original mode, presumably SVC, */ - msr CPSR_c, r2 /* with FIQ/IRQ disable bits forced to 1. */ -#endif -.LC23: - /* Setup a default stack-limit in-case the code has been - compiled with "-mapcs-stack-check". Hard-wiring this value - is not ideal, since there is currently no support for - checking that the heap and stack have not collided, or that - this default 64k is enough for the program being executed. - However, it ensures that this simple crt0 world will not - immediately cause an overflow event: */ -#ifdef THUMB1_ONLY - movs r2, #64 - lsls r2, r2, #10 - subs r2, r3, r2 - mov sl, r2 -#else - sub sl, r3, #64 << 10 /* Still assumes 256bytes below sl. */ -#endif #endif #endif /* Zero the memory in the .bss section. */ @@ -443,10 +557,12 @@ change_back: /* Halt the execution. This code should never be executed. */ /* With no debug monitor, this probably aborts (eventually). With a Demon debug monitor, this halts cleanly. - With an Angel debug monitor, this will report 'Unknown SWI'. */ + With an Angel debug monitor, this will report 'Unknown SWI'. */ swi SWI_Exit #endif + FN_EH_END + /* For Thumb, constants must be after the code since only positive offsets are supported for PC relative addresses. */ .align 0 @@ -464,9 +580,6 @@ change_back: #else .word 0x80000 /* Top of RAM on the PIE board. */ #endif - -.Lstack: - .word __stack .Lhwinit: .word FUNCTION (hardware_init_hook) .Lswinit: @@ -477,19 +590,18 @@ change_back: runtime (meaning "ignore setting") for the variables, when the user does not provide the symbols. (The linker uses a weak symbol if, and only if, a normal version of the same symbol isn't provided - e.g. by a linker script or another object file.) */ + e.g. by a linker script or another object file.) */ - .weak __stack .weak FUNCTION (hardware_init_hook) .weak FUNCTION (software_init_hook) #endif #endif -#if defined(__ELF__) && !defined(__USING_SJLJ_EXCEPTIONS__) - /* Protect against unhandled exceptions. */ - .cantunwind - .fnend -#endif + +.Lstack: + .word __stack + .weak __stack + .LC1: .word __bss_start__ .LC2: |