ff77712a8a
When compiling the s390-ccw bios with clang, it emits a warning like this:
pc-bios/s390-ccw/jump2ipl.c:86:9: warning: indirection of non-volatile null
pointer will be deleted, not trap [-Wnull-dereference]
if (*((uint64_t *)0) & RESET_PSW_MASK) {
^~~~~~~~~~~~~~~~
pc-bios/s390-ccw/jump2ipl.c:86:9: note: consider using __builtin_trap() or
qualifying pointer with 'volatile'
We could add a "volatile" here to shut it up, but on the other hand,
we also have a pointer variable called "reset_psw" in this file already
that points to the PSW at address 0, so we can simply use that pointer
variable instead.
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210423142440.582188-1-thuth@redhat.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
98 lines
2.8 KiB
C
98 lines
2.8 KiB
C
/*
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* QEMU s390-ccw firmware - jump to IPL code
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or (at
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* your option) any later version. See the COPYING file in the top-level
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* directory.
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*/
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#include "libc.h"
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#include "s390-ccw.h"
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#include "s390-arch.h"
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#define KERN_IMAGE_START 0x010000UL
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#define RESET_PSW_MASK (PSW_MASK_SHORTPSW | PSW_MASK_64)
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#define RESET_PSW ((uint64_t)&jump_to_IPL_addr | RESET_PSW_MASK)
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static uint64_t *reset_psw = 0, save_psw, ipl_continue;
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void write_reset_psw(uint64_t psw)
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{
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*reset_psw = psw;
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}
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static void jump_to_IPL_addr(void)
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{
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__attribute__((noreturn)) void (*ipl)(void) = (void *)ipl_continue;
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/* Restore reset PSW */
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write_reset_psw(save_psw);
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ipl();
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/* should not return */
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}
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void jump_to_IPL_code(uint64_t address)
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{
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/* store the subsystem information _after_ the bootmap was loaded */
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write_subsystem_identification();
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write_iplb_location();
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/* prevent unknown IPL types in the guest */
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if (iplb.pbt == S390_IPL_TYPE_QEMU_SCSI) {
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iplb.pbt = S390_IPL_TYPE_CCW;
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set_iplb(&iplb);
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}
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/*
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* The IPL PSW is at address 0. We also must not overwrite the
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* content of non-BIOS memory after we loaded the guest, so we
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* save the original content and restore it in jump_to_IPL_2.
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*/
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if (address) {
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save_psw = *reset_psw;
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write_reset_psw(RESET_PSW);
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ipl_continue = address;
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}
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debug_print_int("set IPL addr to", address ?: *reset_psw & PSW_MASK_SHORT_ADDR);
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/* Ensure the guest output starts fresh */
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sclp_print("\n");
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/*
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* HACK ALERT.
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* We use the load normal reset to keep r15 unchanged. jump_to_IPL_2
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* can then use r15 as its stack pointer.
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*/
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asm volatile("lghi 1,1\n\t"
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"diag 1,1,0x308\n\t"
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: : : "1", "memory");
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panic("\n! IPL returns !\n");
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}
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void jump_to_low_kernel(void)
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{
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/*
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* If it looks like a Linux binary, i.e. there is the "S390EP" magic from
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* arch/s390/kernel/head.S here, then let's jump to the well-known Linux
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* kernel start address (when jumping to the PSW-at-zero address instead,
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* the kernel startup code fails when we booted from a network device).
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*/
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if (!memcmp((char *)S390EP, "S390EP", 6)) {
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jump_to_IPL_code(KERN_IMAGE_START);
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}
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/* Trying to get PSW at zero address (pointed to by reset_psw) */
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if (*reset_psw & RESET_PSW_MASK) {
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/*
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* Surely nobody will try running directly from lowcore, so
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* let's use 0 as an indication that we want to load the reset
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* psw at 0x0 and not jump to the entry.
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*/
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jump_to_IPL_code(0);
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}
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/* No other option left, so use the Linux kernel start address */
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jump_to_IPL_code(KERN_IMAGE_START);
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}
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