@ @ linux_logo in ARM THUMB assembler 0.23 @ @ Originally by @ Vince Weaver @ @ Crazy size-optimization hacks by @ Stephan Walter @ @ assemble with "as -o ll.thumb.o ll.thumb.s" @ link with "ld -o ll_thumb ll.thumb.o" .include "logo.include" @ Optimization progress: @ 1035 - original @ 1031 - not load r3 each time @ 1027 - use "blx" instruction for strcat_r4 (arm5 specific opt) @ 1023 - use "blx" instruction for strcat_r3 @ 1015 - use "blx" instruction for write_stdout @ 1007 - inlined divide function @ 1007 - use "blx" for center and print (only got rid of two bytes, @ hidden by padding) @ 1003 - use r5 instead of r3 to hold uname info pointer @ 995 - restructure strcat to use r4 rather than r1 @ 995 - use r4 to point to /proc/cpinfo (only got rid of 2 bytes) @ 989 - in-line linefeed instead of doing it by hand (first line) @ @ Architectural info @ @ ARM has 31 registers (only 16 visible at a time) @ In thumb, obly r0-r7 are accessible normally @ The BX instruction is used to change into thumb. Bottom bit @ of the target address is the important one. @ + r13 = stack pointer @ + r14 = link register @ + r15 = program counter @ powerful push/pop that can push/pop any combination of r0-r7 in one insn. @ also can push LR and pop that to PC @ Instructions that can use the high registers: @ add, cmp, mov @ "bl" instructions are 32 bits! @ @ syscalls are like EABI syscalls, syscall num is in r7, args in r0-r? @ reading r15 in general gives you current PC+4 @ 6 Status registers (only one visible in userspace) @ - NZCVQ (Negative, Zero, Carry, oVerflow, saturate) @ prefix most instructions to handle the condition codes: @ EQ, NE (equal/not equal) CS, CC (carry set/clear) @ MI, PL (minus/plus) VS, VC (overflow set/clear) @ HI, LS (unsigned higer/lowersame) @ GE, LT (greaterequal,less than) @ GT, LE (greater than, lessthanequal) @ AL (always) @ comment character is a @ # offsets into the results returned by the uname syscall .equ U_SYSNAME,0 .equ U_NODENAME,65 .equ U_RELEASE,65*2 .equ U_VERSION,(65*3) .equ U_MACHINE,(65*4) .equ U_DOMAINNAME,65*5 # offset into the results returned by the sysinfo syscall .equ S_TOTALRAM,16 # Sycscalls .equ SYSCALL_EXIT, 1 .equ SYSCALL_READ, 3 .equ SYSCALL_WRITE, 4 .equ SYSCALL_OPEN, 5 .equ SYSCALL_CLOSE, 6 .equ SYSCALL_SYSINFO, 116 .equ SYSCALL_UNAME, 122 # .equ STDIN,0 .equ STDOUT,1 .equ STDERR,2 .thumb @ use 16-bit thumb instructions .globl _start _start: #========================= # PRINT LOGO #========================= # LZSS decompression algorithm implementation # by Stephan Walter 2002, based on LZSS.C by Haruhiko Okumura 1989 # optimized some more by Vince Weaver @ r0 = temp @ r1 = output_buffer @ r2 = R @ r3 = logo data inputting from @ r4 = temp @ r5 = counter @ r6 = position @ r7 = match length @ r8 = logo end @ r9 = text_addr ldr r1,out_addr @ buffer we are printing to ldr r2,R @ R ldr r3,logo_addr @ r3 points to logo data ldr r0,logo_end_addr mov r8,r0 @ r8 points to logo end ldr r0,text_addr @ r9 points to text buf mov r9,r0 decompression_loop: ldrb r4,[r3] @ load a byte add r3,#1 @ increment pointer mov r5,#0xff @ load top as a hackish 8-bit counter lsl r5,#8 @ shift 0xff left by 8 orr r5,r4 @ or in the byte we loaded test_flags: cmp r3,r8 @ have we reached the end? bge done_logo @ if so, exit lsr r5,#1 @ shift bottom bit into carry flag bcs discrete_char @ if set, we jump to discrete char offset_length: ldrb r0,[r3] @ load a byte add r3,#1 @ increment pointer ldrb r4,[r3] @ load a byte add r3,#1 @ increment pointer @ we can't load halfword @ as no unaligned loads on arm lsl r4,#8 orr r4,r0,r4 @ merge back into 16 bits @ this has match_length and match_position mov r7,r4 @ copy r4 to r7 @ no need to mask r7, as we do it @ by default in output_loop mov r0,#(THRESHOLD+1) lsr r4,#(P_BITS) add r6,r4,r0 @ r6 = (r4 >> P_BITS) + THRESHOLD + 1 @ (=match_length) output_loop: ldr r0,pos_mask @ urgh, can't handle simple constants and r7,r0 @ mask it mov r0,r9 ldrb r4,[r0,r7] @ load byte from text_buf[] add r7,#1 @ advance pointer in text_buf store_byte: strb r4,[r1] @ store a byte add r1,#1 @ increment pointer mov r0,r9 strb r4,[r0,r2] @ store a byte to text_buf[r] add r2,#1 @ r++ ldr r0,NMINUS1 @ grrr no way to get this easier and r2,r0 @ mask r sub r6,#1 @ decement count bne output_loop @ repeat until k>j mov r0,#0xff lsl r0,#8 tst r5,r0 @ are the top bits 0? bne test_flags @ if not, re-load flags b decompression_loop discrete_char: ldrb r4,[r3] @ load a byte add r3,#1 @ increment pointer mov r6,#1 @ we set r6 to one so byte @ will be output once b store_byte @ and store it # end of LZSS code done_logo: ldr r1,out_addr @ buffer we are printing to ldr r0,strcat_addr mov r11,r0 @ point r11 to "strcat_r4" sub r0,#8 mov r10,r0 @ point r10 to "strcat_r3" sub r0,#(strcat_r5-write_stdout) mov r9,r0 @ point r9 to "write_stdout" sub r0,#(write_stdout-center_and_print) mov r8,r0 blx r9 @ print the logo #========================== # PRINT VERSION #========================== first_line: ldr r0,uname_addr mov r5,r0 mov r7,#SYSCALL_UNAME swi #0 @ do uname syscall @ os-name from uname "Linux" ldr r6,out_addr @ point r6 to out_buffer blx r10 @ call strcat_r5 ldr r4,ver_addr @ source is " Version " blx r11 @ call strcat_r4 add r5,#U_RELEASE @ version from uname, ie "2.6.20" blx r10 @ call strcat_r5 @ source is ", Compiled " blx r11 @ call strcat_r4 add r5,#(U_VERSION-U_RELEASE) @ compiled date blx r10 @ call strcat_r5 @ source is "\n" blx r11 @ call strcat_r4 blx r8 @ center and print @=============================== @ Middle-Line @=============================== middle_line: @========= @ Load /proc/cpuinfo into buffer @========= ldr r6,out_addr @ point r6 to out_buffer mov r0,r4 @ '/proc/cpuinfo' mov r1,#0 @ 0 = O_RDONLY mov r7,#SYSCALL_OPEN swi #0 @ syscall. return in r0? mov r3,r0 @ save our fd ldr r1,disk_addr mov r2,#128 lsl r2,#5 @ 4096 is maximum size of proc file ;) mov r7,#SYSCALL_READ swi #0 mov r0,r3 mov r7,#SYSCALL_CLOSE swi #0 @ close (to be correct) @============= @ Number of CPUs @============= number_of_cpus: @ cheat. Who has an SMP arm? @ Print "One" add r4,#14 @ length of /proc/cpuinfo blx r11 @ call strcat_r4 @========= @ MHz @========= print_mhz: @ the arm system I have does not report MHz @========= @ Chip Name @========= chip_name: mov r0,#'s' mov r1,#'o' mov r2,#'r' mov r3,#' ' bl find_string @ find 'sor\t: ' and grab up to ' ' blx r11 @ print " Processor, " @======== @ RAM @======== ldr r0,sysinfo_addr mov r2,r0 mov r7,#SYSCALL_SYSINFO swi #0 @ sysinfo() syscall add r2,#S_TOTALRAM ldr r3,[r2] @ size in bytes of RAM lsr r3,#20 @ divide by 1024*1024 to get M mov r0,#1 bl num_to_ascii @ print 'M RAM, ' blx r11 @ call strcat @======== @ Bogomips @======== mov r0,#'I' mov r1,#'P' mov r2,#'S' mov r3,#'\n' bl find_string blx r11 @ print bogomips total blx r8 @ center and print #================================= # Print Host Name #================================= last_line: ldr r6,out_addr @ point r6 to out_buffer sub r5,#(U_VERSION-U_NODENAME) @ host name from uname() blx r10 @ call strcat_r5 blx r8 @ center and print ldr r1,colors_addr @ restore colors, print a few linefeeds blx r9 @ write_stdout @================================ @ Exit @================================ exit: mov r0,#0 @ result is zero mov r7,#SYSCALL_EXIT swi #0 @================================= @ FIND_STRING @================================= @ r0,r1,r2 = string to find @ r3 = char to end at @ writes to r6 find_string: push {r5,r7,lr} ldr r7,disk_addr @ look in cpuinfo buffer find_loop: ldrb r5,[r7] @ load a byte cmp r5,#0 @ off the end? beq done @ then finished add r7,#1 @ increment pointer cmp r5,r0 @ compare against first byte bne find_loop ldrb r5,[r7] @ load next byte cmp r5,r1 bne find_loop @ if not equal, loop ldrb r5,[r7,#1] @ load next byte cmp r5,r2 bne find_loop @ if not equal, loop @ if all 3 matched, we are found find_colon: ldrb r5,[r7] @ load a byte add r7,#1 @ increment pointer cmp r5,#':' bne find_colon @ repeat till we find colon add r7,r7,#1 @ skip the space store_loop: ldrb r5,[r7] @ load a byte, increment pointer strb r5,[r6] @ store a byte, increment pointer add r7,#1 @ increment pointers add r6,#1 cmp r5,r3 bne store_loop almost_done: mov r0,#0 strb r0,[r6] @ replace last value with NUL sub r6,#1 @ adjust pointer done: pop {r5,r7,pc} @ return #============================== # center_and_print #============================== # string to center in at output_buffer center_and_print: push {r3,r4,LR} @ store return address on stack ldr r1,colors_addr @ we want to output ^[[ mov r2,#2 bl write_stdout_we_know_size str_loop2: ldr r2,out_addr @ point r2 to out_buffer sub r2,r2,r6 @ get length by subtracting @ actually, negative value here @ an optimization... @ subtract r2 from 81 add r2,#81 @ we use 81 to not count ending \n blt done_center @ if result negative, don't center lsr r3,r2,#1 @ divide by 2 mov r0,#0 @ print to stdout bl num_to_ascii @ print number of spaces add r1,#7 @ we want to output C blx r9 @ write_stdout done_center: ldr r1,out_addr @ point r1 to out_buffer blx r9 @ write_stdout pop {r3,r4,PC} @ restore return address from stack @############################# @ num_to_ascii @############################# @ r3 = value to print @ r0 = 0=stdout, 1=strcat num_to_ascii: push {r1,r2,r3,r4,r5,LR} @ store return address on stack ldr r2,ascii_addr add r2,#9 @ point to end of our buffer mov r7,#10 @ we'll be dividing by 10 div_by_10: @=================================================== @ Divide - because ARM has no hardware int divide @ yes this is an awful algorithm, but simple @ and uses few registers @================================================== @ r3=numerator r7=denominator @ r5=quotient r4=remainder divide: mov r5,#0 @ zero out quotient divide_loop: mov r1,r5 @ move Q temporarily to r2 mul r1,r7 @ multiply Q by denominator add r5,#1 @ increment quotient cmp r1,r3 @ is it greater than numerator? ble divide_loop @ if not, loop sub r5,#2 @ otherwise went too far, decrement @ and done mov r1,r5 @ move Q temporarily to r2 mul r1,r7 @ calculate remainder sub r4,r3,r1 @ R=N-(Q*D) @ bl divide @ Q=r5, R=r4 add r4,#0x30 @ convert to ascii strb r4,[r2] @ store a byte sub r2,#1 @ decrement pointer mov r3,r5 @ move Q in for next divide, update flags bne div_by_10 @ if Q not zero, loop write_out: add r1,r2,#1 @ adjust pointer cmp r0,#0 beq num_stdout mov r5,r1 blx r10 @ if 1, strcat_r5 pop {r1,r2,r3,r4,r5,pc} @ pop and return num_stdout: blx r9 @ else, fallthrough to stdout pop {r1,r2,r3,r4,r5,pc} @ pop and return #================================ # strcat #================================ # value to cat in r4 # output buffer in r6 # r3 trashed strcat_r5: push {r4,lr} mov r4,r5 blx r11 pop {r4,pc} strcat_r4: push {r3,lr} strcat_loop: ldrb r3,[r4] @ load a byte add r4,#1 @ increment pointer strb r3,[r6] @ store a byte add r6,#1 @ increment pointer cmp r3,#0 @ is it zero? bne strcat_loop @ if not loop sub r6,r6,#1 @ point to one less than null pop {r3,pc} @ return #================================ # WRITE_STDOUT #================================ # r1 has string # r0,r2,r3 trashed write_stdout: mov r2,#0 @ clear count str_loop1: add r2,#1 ldrb r3,[r1,r2] cmp r3,#0 bne str_loop1 @ repeat till zero write_stdout_we_know_size: mov r0,#STDOUT @ print to stdout mov r7,#SYSCALL_WRITE swi #0 @ run the syscall bx lr @ return .align 2 @ data address ver_addr: .word ver_string colors_addr: .word default_colors logo_addr: .word logo logo_end_addr: .word logo_end @bss addresses uname_addr: .word uname_info sysinfo_addr: .word sysinfo_buff ascii_addr: .word ascii_buffer text_addr: .word text_buf disk_addr: .word disk_buffer out_addr: .word out_buffer @ constant values pos_mask: .word ((POSITION_MASK<<8)+0xff) R: .word (N-F) NMINUS1: .word (N-1) @ function pointers strcat_addr: .word (strcat_r4+1) @ +1 to make it a thumb addr .align 1 #=========================================================================== # section .data #=========================================================================== .data ver_string: .asciz " Version " compiled_string:.asciz ", Compiled " linefeed: .asciz "\n" .ifdef FAKE_PROC cpuinfo: .asciz "proc/cpui.arm" .else cpuinfo: .asciz "/proc/cpuinfo" .endif one: .asciz "One " processor: .asciz " Processor, " ram_comma: .asciz "M RAM, " bogo_total: .asciz " Bogomips Total\n" default_colors: .asciz "\033[0m\n\n" C: .asciz "C" .include "logo.lzss_new" #============================================================================ # section .bss #============================================================================ .bss bss_begin: .lcomm uname_info,(65*6) .lcomm sysinfo_buff,(64) .lcomm ascii_buffer,10 .lcomm text_buf, (N+F-1) .lcomm disk_buffer,4096 @ we cheat!!!! .lcomm out_buffer,16384 # see /usr/src/linux/include/linux/kernel.h